,the ,geological ,society of ,america ,special ,paper #fe ,,the ,,floors ,,of ,,the ,,oceans ,i4 ,,the ,,north ,,atlantic ,text to ,accompany the ,physiographic ,diagram of the ,north ,atlantic ,,by ,,bruce ,c4 ,,heezen1 ,,marie ,,tharp1 ,,and ,,maurice ,,ewing ,lamont ,geological ,observatory 7,columbia ,university7 ,palisades1 ,new ,york ,illustration ,april #aa1 #aiei ,made in the ,united ,states of ,america ,,text ,,pages ,,composed ,,and ,,printed ,,by ,,the ,,william ,,byrd ,,press ,,collotype ,,plates ,,printed ,,by ,,the ,,meriden ,,gravure ,,company ,,line ,,plates ,,printed ,,by ,,williams ,,and ,,heintz ,,bound ,,by ,,russell-,,rutter ,,company ,,published ,,by ,,the ,,geological ,,society ,,of ,,america ,,address ,,all ,,communications ,,to ,,the ,,geological ,,society ,,of ,,america #dai ,,west #aag ,,street1 ,,new ,,york #bg1 ,n4 ,y4 ,the ,special ,papers ,series ,of ,the ,geological ,society of ,america is made possible through the bequest of ,richard ,alexander ,fullerton ,penrose1 ,jr4 ,could the waters of the ,atlantic be drawn off1 so as to expose to view this great sea-gash1 which separates continents1 and extends from the ,arctic to the ,antarctic1 it would present a scene the most rugged1 grand1 and imposing4 ,the very ribs of the solid earth1 with the foundations of the sea1 would be brought to light1 and we should have presented to us at one view the empty cradle of the ocean4444 7,m4 ,f4 ,maury1 ,the ,physical ,geography of the ,sea1 #ahee47 ,,foreword ,the diagrammatic portrayal of the relief of continental land areas of the world has been completed by both the late ,a4 ,k4 ,lobeck and ,erwin ,raisz1 whose magnificent diagrams are familiar to all geologists and geographers4 ,the authors of the present sheet are preparing a similar series of marine physiographic diagrams4 ,the ,physiographic ,diagram3 ,atlantic ,ocean2 ,sheet #a is the first of this projected series4 ,the ,atlantic ,ocean diagram will consist of five sheets at a scale of about #a3e million4 ,a diagram of the ,south ,atlantic ,ocean at a scale of about #a3aa million now nearly completed will form the first of a general series planned to portray the world oceans4 ,in addition1 diagrams of selected areas well covered by sounding profiles will be prepared at scales of about #a3b million4 ,each sheet or series of sheets will be accompanied by descriptive notes treating the nomenclature1 morphological1 geological1 and geophysical characteristics of each of the physiographic provinces4 ,lamont ,geological ,observatory ,contribution #cjh ,,note ,physiographic ,diagram3 ,atlantic ,ocean1 ,sheet #a 7,plate #a7 ,copies of the ,physiographic ,diagram3 ,atlantic ,ocean1 ,sheet #a are available unfolded so that each will be suitable for wall mounting4 ,the diagram is therefore not physically inserted or attached to this volume although it forms the basic part of the paper4 ,,acknowledgements ,the studies of submarine topography at the ,lamont ,geological ,observatory have been supported by the ,united ,states ,navy ,bureau of ,ships under ,contract ,n,obsr #fdedg4 ,the expeditions which obtained topographic data were supported by the ,office of ,naval ,research under ,contracts ,n#f onr #bgabd and ,n#f onr #bgaac and the ,bureau of ,ships under ,contract ,n,obsr #fdedg4 ,three cruises were supported by the ,national ,geographic ,society1 the ,woods ,hole ,oceanographic ,institution1 and ,columbia ,university4 ,financial support has been received from ,the ,geological ,society of ,america 7,grant #fce-ed74 ,the preparation of this paper was supported in part by the ,bell ,telephone ,laboratories4 ,the studies that led to the present paper began at the ,woods ,hole ,oceanographic ,institution just after ,world ,war ,,ii4 ,with the founding of the ,lamont ,geological ,observatory in #aidi the work was transferred to that observatory at ,palisades1 ,new ,york4 ,topographic data from ,woods ,hole cruises were incorporated with ,lamont data until #aiec1 when a separate program was established at ,woods ,hole by ,j4 ,b4 ,hersey1 and ,columbia ,university acquired the ,,vema as its own research vessel4 ,although ,woods ,hole data obtained between #aiec and #aieg have not been used in preparing sheet #a1 arrangements recently concluded provide for the incorporation of past and future ,woods ,hole data in subsequent sheets of this series4 ,the soundings were read1 compiled1 and plotted by ,morris ,wirshup1 the late ,andrew ,nelson1 ,ivan ,tolstoy1 ,g4 ,leonard ,johnson1 ,,iii1 the authors1 and several others4 ,the profiles were plotted by ,m4 ,wirshup1 ,hester ,haring1 the authors1 and several others4 ,the soundings were taken primarily on board the ,research ,vessels ,,vema and ,,atlantis 7,woods ,hole ,oceanographic ,institution71 but important sounding lines were obtained by the ,r_/,v ,,albatross 7,woods ,hole ,oceanographic ,institution71 ,m_/,v ,,theta1 and ,r_/,v ,,caryn 7,woods ,hole ,oceanographic ,institution7 and in the eastern ,atlantic by the ,r4,r4,s4 ,,discovery 7,national ,institute of ,oceanography74 ,the following officers made outstanding contributions to the navigational plotting3 ,a4 ,k4 ,lane1 the late ,a4 ,karlson1 ,j4 ,pike1 ,r_/,v ,,atlantis2 ,d4 ,gould1 the late ,f4 ,s4 ,usher1 ,d4 ,smith1 ,v4 ,sinclair1 ,h4 ,kohler1 and ,k4 ,simonson1 ,r_/,v ,,vema2 and the late ,a4 ,nelson1 ,r_/,v ,,vema and ,m_/,v ,,theta4 ,the echo sounders have been installed1 maintained1 and improved by ,b4 ,luskin1 ,h4 ,r4 ,johnson1 ,a4 ,roberts1 ,m4 ,landisman1 ,c4 ,hubbard1 ,h4 ,van ,santford1 ,m4 ,langseth1 ,g4 ,sutton1 and many others4 ,the entire scientific party of each of the more than #ej expeditions represented in the data of this paper took turns marking and adjusting the echo sounder1 and all navigational officers on these expeditions took the fixes and kept the logs4 ,to these sea-going scientists and mariners too numerous to list the authors are extremely grateful4 ,soundings in the northeast ,atlantic compiled by the ,british ,admiralty ,hydrographic ,department were kindly provided by ,cmdr4 ,j4 ,s4 ,n4 ,pryor of that organization4 ,dr4 ,m4 ,n4 ,hill of ,cambridge and ,dr4 ,g4 ,e4 ,r4 ,deacon of the 7,british7 ,national ,institute of ,oceanography were instrumental in obtaining many of these valuable deep-sea soundings4 ,original sounding sheets of many areas were provided by the ,coast and ,geodetic ,survey through the courtesy of ,admiral ,a4 ,karo and ,mr4 ,g4 ,f4 ,jordan4 ,b4 ,luskin's development of the ,precision ,depth ,recorder and his continued research and development in echo-sounding equipment made it possible to obtain many of the detailed data of this paper4 ,the following expedition chief scientists conducted sounding surveys which have been incorporated in this paper3 ,m4 ,ewing1 ,j4 ,l4 ,worzel1 ,j4 ,e4 ,nafe1 ,i4 ,tolstoy1 ,r4 ,s4 ,edwards1 ,g4 ,r4 ,hamilton1 ,c4 ,l4 ,drake1 ,b4 ,luskin1 ,w4 ,c4 ,beckmann1 ,f4 ,press1 ,j4 ,northrop1 ,j4 ,hirshman1 ,m4 ,j4 ,davidson1 ,r4 ,j4 ,menzies1 ,f4 ,c4 ,fuglister1 ,e4 ,t4 ,miller1 and ,b4 ,c4 ,heezen4 ,the writers are grateful to the great number of scientists who encouraged them in this work and especially to those who offered suggestions and discussed the data and conclusions4 ,we are particularly indebted to ,w4 ,h4 ,bucher for discussions relative to tectonics1 to ,david ,b4 ,ericson for problems relating to sediment distribution and analysis1 and to ,c4 ,o',d4 ,iselin and ,c4 ,h4 ,elmendorf for general encouragement and support during the several years of this study4 ,,contents ,,page ,,abstract #a ,,part #a4 ,,preparation ,,of ,,the ,,physiographic ,,diagram #c ,,part #b4 ,,physiographic ,,provinces #aa ,introduction #aa ,nomenclature and classification of deep-sea relief #aa ,units of depth and slope #ab ,continent and ocean #af ,continental margin #ag ,definition and general categories #ag ,general categories #ag ,category ,i provinces #ag ,category ,,ii provinces #ah ,category ,,iii provinces #ai ,regional description of continental margin #ba ,benches and terraces of the continental margin #da ,geology and geophysics of continental-margin physiographic provinces #ea ,seismicity of the continental-margin provinces #ea ,magnetic anomalies and continental-margin physiographic provinces #ea ,crustal structures and continental-margin provinces #eb ,sediment distribution and physiographic provinces of the continental margin #ec ,past1 present1 and future of the continental-margin provinces #ec ,ocean-basin floor #ee ,general description #ee ,abyssal plains #ee ,general discussion #ee ,regional description #eg ,abyssal hills #fa ,definition and distribution #fa ,regional description #fc ,origin of abyssal-hills topography #fe ,other major features of the abyssal floor #ff ,abyssal gaps #ff ,mid-ocean canyons #ff ,regional description #ff ,origin of abyssal-floor topography #gd ,oceanic rises #gd ,definition and distribution #gd ,regional description #gd ,seamounts of the ocean-basin floor #gh ,seismicity of the ocean-basin floor #hj ,ocean-basin floor provinces and crustal structure #hj ,mid-oceanic ridges #hc ,definition #hc ,mid-,atlantic ,ridge #hc ,provinces of the ,mid-,atlantic ,ridge #hd ,general statement #hd ,crest provinces #hd ,flank provinces #ie ,azores ,plateau #ig ,azores-,gibraltar ,ridge #ih ,atlantis-,plato-,cruiser-,great ,meteor ,seamount ,chain #ih ,geology and geophysics of ,mid-,atlantic ,ridge physiographic provinces #ih ,seismicity of the ,mid-,atlantic ,ridge #ih ,sediments and physiographic provinces of the ,mid-,atlantic ,ridge #ii ,rocks of the ,mid-,atlantic ,ridge #ii ,crustal structure of the ,mid-,atlantic ,ridge provinces #ajj ,origin of the ,mid-,atlantic ,ridge #ajc ,sub-bottom reflections recorded on ,,pdr records and physiographic provinces #je ,summary of province characteristics #ajg ,,bibliography #aji ,,index #aae ,,illustrations ,,plates ,,following ,,plate ,,page #a4 ,physiographic diagram3 ,atlantic ,ocean1 ,sheet #a 7,in separate tube7 #b4 ,preliminary chart of ,hudson ,submarine ,canyon #bj #c4 ,representative ,,pdr records from continental rise of northeastern ,united ,states #cb #d4 ,,pdr records from continental slope and ,blake ,plateau #cb #e4 ,,pdr records from outer ridge east of the ,blake ,plateau and from the ,blake-,bahama ,abyssal ,plain #cb #f4 ,,pdr record of outer ridge showing sub-bottom horizon #cb #g4 ,tracings of ,,pdr records across continental slope and part of the ,blake ,plateau #cf #h4 ,,pdr records ,european continental rise and ,biscay ,abyssal ,plain #ch #i4 ,representative ,,pdr records of continental margin and abyssal floor southwest of ,canary ,islands #ch #aj4 ,,pdr record of abyssal hills1 southeast of ,bermuda ,rise #ch #aa4 ,ocean bottom photographs of the continental margin and ocean basin floor #ch #ab4 ,,pdr record of ,biscay ,abyssal ,plain #eb #ac4 ,,pdr records of ,madeira ,abyssal ,plain and the ,madeira ,rise #eb #ad4 ,,pdr records of ,mid-,ocean ,canyon ,no4 #b and canyons at ,vema ,gap #eh #ae4 ,ocean-bottom photographs of seamounts #eh #af4 ,representative ,,pdr records from ,bermuda ,rise #gh #ag4 ,,pdr record1 ,bermuda ,scarp ,zone #gh #ah4 ,,pdr record1 ,upper ,step ,mid-,atlantic ,ridge #gh #ai4 ,ocean-bottom photographs2 ,mid-,atlantic ,ridge #gh #bj4 ,physiographic provinces1 ,atlantic ,ocean #abb #ba4 ,control chart #abb #bb4 ,six trans-,atlantic topographic profiles #abb #bc4 ,index chart showing locations of profiles of ,plates #bd1 #be1 #bf and ,figure #de #abb #bd4 ,thirty-four profiles of the continental margin3 western ,north ,atlantic #abb #be4 ,twenty-three profiles of the continental margin of ,europe and ,africa #abb #bf4 ,crustal structure and continental-margin provinces #abb #bg4 ,five topographic profiles1 western ,north ,atlantic #abb #bh4 ,distribution of deep-sea sands in relation to physiographic provinces #abb #bi4 ,earthquake epicenters1 ,north ,atlantic #abb #cj4 ,location of ,,pdr records and bottom photographs reproduced as illustrations4 #abb ,,figures ,,page ,,figure #a4 ,method of preparation of physiographic diagram #d #b4 ,precision depth recorder 7,,pdr7 sounding lines obtained by research vessels #f #c4 ,good1 but nonprecision sounding lines obtained by research vessels #g #d4 ,major basins of the ,north ,atlantic1 after ,wst 7#aidj7 #ab #e4 ,sound-velocity corrections for echo soundings #ac #f4 ,conversion diagram for degrees1 per cent grade1 feet per statute mile1 and gradient #ad #g4 ,gradients from #a3e to #a3hjjj shown at #dj3a vertical exaggeration #ae #h4 ,outline of submarine topography #ae #i4 ,major morphologic divisions3 ,north ,atlantic ,ocean #af #aj4 ,three categories of continental-margin provinces #ag #aa4 ,two east-west profiles of ,southeast ,newfoundland ,ridge #bb #ab4 ,laurentian ,channel #bc #ac4 ,eastern ,channel1 ,gulf of ,maine #bc #ad4 ,submarine canyons off the ,scotian ,shelf #bd #ae4 ,continental-margin provinces3 ,type profile off northeastern ,united ,states #bf #af4 ,tracings of ,,pdr records of continental and insular slopes #bh #ag4 ,cross sections of ,hudson ,submarine ,canyon #cb #ah4 ,tracing of ,,pdr record of ,blake ,escarpment #cd #ai4 ,continental-margin provinces3 ,type profiles off northwest ,africa #dj #bj4 ,georges ,bank canyons #dd #ba4 ,two projected profiles of ,georges ,bank canyons #de #bb4 ,geologic section at ,cape ,hatteras1 ,virginia #df #bc4 ,correlation of structural benches off northeast ,united ,states #dh #bd4 ,geologic section3 ,western ,europe based on refraction measurements #di #be4 ,index chart1 location of abyssal hill profiles illustrated in ,figures #bf and #bg #fb #bf4 ,eleven profiles1 ,abyssal ,hills ,province1 western ,atlantic #fb #bg4 ,eight profiles1 ,abyssal ,hills ,province1 eastern ,atlantic #fc #bh4 ,tracing of ,,pdr record1 abyssal hills1 southeast of ,bermuda ,rise #fd #bi4 ,northwest ,atlantic ,mid-,ocean ,canyon #fg #cj4 ,eight east-west profiles showing ,northwest ,atlantic ,mid-,ocean ,canyon #fh #ca4 ,forty-eight cross sections of ,northwest ,atlantic ,mid-,ocean ,canyon #fi #cb4 ,long profile of ,northwest ,atlantic ,mid-,ocean ,canyon #gj #cc4 ,tracing of ,,pdr record across ,theta ,gap #gc #cd4 ,natural scale profile1 ,kelvin ,seamounts #gg #ce4 ,crustal sections in various physiographic provinces1 determined by seismic-refraction measurements #ha #cf4 ,index to natural-scale ,mid-,atlantic ,ridge profiles reproduced in ,figures #cg-da #hd #cg4 ,natural-scale ,mid-,atlantic ,ridge profile #a;,a #he #ch4 ,natural-scale ,mid-,atlantic ,ridge profile #a;,b #hf #ci4 ,natural-scale ,mid-,atlantic ,ridge profile #a;,c #hg #dj4 ,natural-scale ,mid-,atlantic ,ridge profile #b;,a #hh #da4 ,natural-scale ,mid-,atlantic ,ridge profile #b;,b #hi #db4 ,type profile1 provinces of the ,mid-,atlantic ,ridge #ij #dc4 ,tracing of ,,pdr record1 ,rift ,valley1 ,rift ,mountains1 ,high ,fractured ,plateau1 and ,upper ,step #ia #dd4 ,tracing of ,,pdr record1 ,western ,rift ,mountains #ib #de4 ,twenty-six rift valley profiles1 ,mid-,atlantic ,ridge #ic #df4 ,five representative profiles1 crest and western flank of ,mid-,atlantic ,ridge #id #dg4 ,axial profile of the ,mid-,atlantic ,ridge #if #dh4 ,profile of total magnetic intensity and topography1 ,mid-,atlantic ,ridge #aja #di4 ,physiographic provinces and trans-,atlantic structure #ajb ,,tables ,,table ,,page #a4 ,characteristics of continental rise1 northeastern ,united ,states #bg #b4 ,characteristics of continental rise1 northwest ,africa #da #c4 ,depths of prominent continental-shelf terraces #db ,,abstract ,the ,physiographic ,diagram3 ,atlantic ,ocean1 ,sheet #a1 which portrays the ,north ,atlantic between #ag and #ej ,north ,latitude1 is the first of a projected series of diagrams4 ,the diagram is based on continuous echo-sounding traverses made by research vessels4 ,the relief shown on the profiles was sketched in perspective using the technique introduced by ,lobeck4 ,between sounding profiles the relief is speculative1 based on extrapolation of trends noted in the profiles4 ,the area of the diagram is divided into three major physiographic regions which are in turn subdivided into the following categories of provinces4 ,,continental ,,margin ,category ,i ,continental ,shelf ,epicontinental ,seas ,marginal ,plateaus ,category ,,ii ,continental ,slope ,marginal ,escarpments ,landward ,slopes of ,trenches ,category ,,iii ,continental ,rise ,marginal ,trench-,outer ,ridge ,complex ,marginal ,basin-,outer ,ridge ,complex ,,ocean ,,basin ,,floor ,abyssal ,floor ,abyssal ,plains ,abyssal ,hills ,abyssal ,gaps and ,mid-,ocean ,canyons ,oceanic ,rises ,seamount ,groups ,,mid-,,oceanic ,,ridge ,crest ,provinces ,rift ,valley ,rift ,mountains ,high ,fractured ,plateau ,flank ,provinces ,upper ,step ,middle ,step ,lower ,step ,each province is defined1 briefly described1 and illustrated with profiles and photographs of echo-sounding records4 ,the boundaries of the physiographic provinces1 defined solely by bottom topography1 show good correlation with variations in crustal structure as determined by seismic-refraction measurements and with anomalies of the gravity and magnetic fields4 ,in addition1 the province boundaries correlate well with distribution patterns of bottom sediments4 ,the physiographic provinces are thus really morpho-tectonic provinces4 ,the precise correlation of topographic provinces and structure observed in specific sections can thus be extrapolated along province boundaries to deduce the geology in large areas where no geophysical work has been done4 ,the tectonic map of the ,atlantic prepared in this manner will be presented in a subsequent publication4 ,,part #a4 ,,preparation ,,of ,,the ,,physiographic ,,diagram ,several steps are involved in the preparation of a marine physiographic diagram4 ,the raw data consist of continuously recorded echograms and lists of positions of the research ship4 ,echograms are profiles of ocean depth1 automatically plotted against time 7,luskin et al41 #aied74 ,the first step is to read and tabulate the depth at each peak1 trough1 or change of slope4 ,these readings are plotted on a chart 7#a3a1jjj1jjj7 as a series of closely spaced soundings4 ,depth profiles are plotted against distance at a standard vertical exaggeration of #dj3a4 ,the sounding lines are also plotted on a chart of small scale 7#a3e1jjj1jjj7 which is at the same scale as the final physiographic diagram4 ,the subsequent steps in the preparation of the diagram are illustrated by ,figures #a;a-d4 ,the exaggerated profiles 7#a;b7 along the tracks 7#a;a7 show a succession of peaks and valleys4 ,these features are sketched in along the tracks 7#a;c74 ,after all the tracks in a large area are sketched in this way1 the major trends are estimated1 and the diagram is completed by interpolation and extrapolation 7,fig4 #a;d2 ,pl4 #a74 ,the vertical scale of the diagram is #a inch #ejjj fathoms which is an effective vertical exaggeration of #bj to #a4 ,the final diagram as printed is at a scale of #a3e million at #dj ,n4 on a ,mercator projection4 ,there is a fundamental difference between the preparation of a terrestrial and a marine physiographic diagram4 ,in the former the major problem is to select from more-detailed maps the features to be represented4 ,except in unexplored1 inaccessible areas1 the shape of all land features is a matter of recorded fact2 the problem is to abstract and artfully draw the features in question4 ,in contrast1 the preparation of a marine physiographic diagram requires the author to postulate the patterns and trends of the relief on the basis of cross sections and then to portray this interpretation in the diagram4 ,,physiographic ,,province ,,chart3 ,a study of the exaggerated profiles plotted during the preparation of the physiographic diagram revealed the existence of morphological features and morphological provinces not previously delineated4 ,the limits of areas of contrasting morphology were noted on the profiles1 and these points were plotted on a chart of small scale 7also about #a3e million at #dj ,n47 7,pl4 #bj74 ,,control3 ,almost all the echo-sounding profiles used in the preparation of the physiographic diagram 7,pl4 #a7 and the physiographic province chart 7,pl4 #bj7 were obtained by expeditions of the ,lamont ,geological ,observatory and the ,woods ,hole ,oceanographic ,institution 7,pl4 #ba74 ,some soundings were provided by the ,hydrographic ,department1 ,british ,admiralty 7,pl4 #ba7 and the ,international ,hydrographic ,bureau 7,monaco74 ,illustration3 ,,figure #a4--,method of preparation of physiographic diagram 7a7 ,positions of sounding lines 7,a1 ,b7 are plotted on chart2 7b7 ,soundings are plotted as profiles 7,a1 ,b7 at #dj3a vertical exaggeration2 7c7 ,features shown on profiles 7,a1 ,b7 are sketched on chart along tracks2 7d7 ,after all available sounding profiles are sketched the remaining unsounded areas are filled in by extrapolating and interpolating trends observed in a succession of profiles4 ,the echo soundings made by research vessels fall into three classes3 7#a7 precision soundings 7accuracy better than #a fathom in #cjjj72 7#b7 nonprecision soundings obtained by research vessels using commercial echo sounders with control or close check on time standard2 7#c7 poor to bad soundings made with commercial echo sounders without timing control or adequate checks4 ,most of the soundings used in this paper fall into the first two categories4 ,in ,figure #b the ,precision ,depth ,recorder 7,,pdr7 sounding tracks are shown4 ,in ,figure #c the good but nonprecision tracks are shown4 ,the soundings of the third class are not shown4 ,all tracks used in the preparation of the diagram are shown in ,plate #ba4 ,most of the sounding lines were located by standard dead-reckoning procedures from astronomical fixes4 ,errors of a few miles are probably common4 ,position errors do not seriously affect the work described here since we are dealing largely with texture read from profiles and plotted on a small-scale sheet4 ,in addition to the sounding tracks shown in the control chart1 spot depths shown on ,u4 ,s4 ,hydrographic ,office charts ,,ho #jiee;a1 #jiee;b1 #jief;a1 #jief;b1 and #edhg and on feuille ,a-#a of the ,carte ,gnrale ,bathymtrique des ,ocans 7#aice7 were used where profiles were lacking4 ,along the east coast of the ,united ,states the ,coast and ,geodetic ,survey soundings published by ,veatch and ,smith 7#aici7 were used for the continental shelf and slope4 ,other important sources of published soundings include ,hill 7#aief71 ,de ,andrade 7#aicg71 ,dietrich 7#aici71 ,wst 7#aidj;a71 ,emery 7#aiej71 and ,tolstoy 7#aiea74 ,the land areas of the diagram were sketched to the same rigid vertical scale as that used for the deep sea4 ,elevations for the ,united ,states were taken from ,united ,states ,geological ,survey and ,army ,map ,service quadrangle maps2 elevations for ,europe and ,africa are from ,bartholomew maps2 and elevations for the islands from ,united ,states ,navy ,hydrographic ,office charts4 ,,exaggerated ,,profiles3 ,the profiles plotted at #dj3a vertical exaggeration are the basis for the topography sketched on the physiographic diagram4 ,a selection of these profiles is reproduced in ,plates #bb1 #bd1 #be1 and #bg1 and in ,figure #de4 ,all profiles from precision soundings were originally plotted at a vertical scale of #b inches equals #ajjj fathoms and a horizontal scale of #b inches equals #dj miles4 ,nonprecision soundings were plotted at scales of #a inch equals #ajjj fathoms and #a inch equals #dj miles4 ,in a typical area #dj to #fj soundings were plotted for each #fj miles of profile4 ,the points were connected and then qualitatively checked against the original echogram4 ,although all the larger features are represented on these profiles1 features of less than a mile in width may be missed4 ,the small scale of the physiographic diagram excluded the possibility of portraying most of the features less than #c-f miles in width and less than #bj fathoms in height4 ,detailed study of the small-scale features less than #b or #c miles in width is best accomplished by a study of the original echograms4 ,the ,,pdr records are ideal for this purpose4 ,illustration3 ,,figure #b4--,precision depth recorder 7,,pdr7 sounding lines obtained by research vessels ,most of soundings shown were obtained by the ,lamont ,geological ,observatory's ,r4 ,v4 ,,vema1 #aiec-aieg4 ,illustration3 ,,figure #c4--;,good1 but nonprecision sounding lines obtained by research vessels ,most soundings obtained by the ,woods ,hole ,oceanographic ,institution's ,r4 ,v4 ,,atlantis1 #aidf-aiec4 ,,north ,,atlantic ,,soundings3 ,the study of the ,north ,atlantic deep-sea bathymetry began a little more than a century ago with the taking of the first deep-sea soundings by lead line4 ,by #ahfj1 largely because of the great public interest in the proposed trans-,atlantic cables and the enthusiastic encouragement of ,matthew ,f4 ,maury 7#ahee71 several hundred soundings had been taken in the ,north ,atlantic in depths greater than #ajjj fathoms4 ,meanwhile1 on either side of the ,atlantic surveys of coasts1 harbors1 offshore banks1 and the continental shelf were being made for navigational use4 ,the ,hudson ,submarine ,channel and the head of the ,hudson ,canyon were discovered by the ,united ,states ,coast ,survey during this period4 ,by #aiab more than #ahjj deep-sea soundings had been taken in the ,north ,atlantic by the laborious method of using a lead lowered at first by hemp line and later by wire4 ,between #aijj and #aibj ,fessenden in the ,united ,states1 ,behm in ,germany1 and ,langevin and ,florisson in ,france established that acoustic echo sounding was possible and built machines to take echo soundings4 ,in #aibb1 echo sounding became a practical operation4 ,although many of the early echo sounders were fitted with automatic recorders1 they were in general suitable only for use in shallow water 7less than #ejj fathoms74 ,deep-sea echo soundings were obtained by listening on earphones for the returning echo and timing the interval by eye with a suitable clock4 ,the improvement of sounding gear continued1 and by the mid #aicj's automatic recording deep-sea echo sounders were manufactured and put into limited use1 although1 by and large1 all pre-,world ,war ,,ii deep-sea 7 #ajjj fathoms7 echo soundings were discrete observations by the ear and eye method4 ,a good review of pre-,world ,war ,,ii echo-sounding apparatus is given in a publication of the ,international ,hydrographic ,bureau 7,anon41 #aici74 ,during the war the ,,nmc#a echo sounder was developed and installed on many ,u4 ,s4 ships4 ,it was adequate for deep-sea sounding if in perfect condition2 but the designers1 being cautious1 had arranged for recording only in the depth range of #j-bjjj fathoms4 ,the ,,nmc sounder on ,atlantis was modified to record in greater depths in #aide1 and many thousands of miles of tracks were obtained of the deep sea with this apparatus4 ,the ,,nmc had a small record chart 7#f inches #bjjj fathoms2 inch about #c miles74 ,the precision was low since the apparatus depended on a ship's regular ,,ac power supply for its time standard4 ,a new sounder1 the ,,uqn-#a;,b1 was developed in the ,united ,states following ,world ,war ,,ii4 ,the instrument as manufactured recorded on an extremely small chart 7#h inches #fjjj fathoms7 but could be modified for multiple #fjj-;fathom scale recording 7#h inches #fjj fathoms74 ,the timing function was usually accomplished by poorly regulated ship's ,,ac power supply1 and errors were consequently large 7,dietz1 #aied2 ,heezen1 #aied74 ,in addition1 the stylus arrangement required constant adjustment4 ,after only a few thousand miles were obtained by the ,lamont ,observatory expeditions it became obvious that a new recorder incorporating precision timing and large recorder presentation was necessary for an adequate knowledge of topography4 #a ,u4 ,s4 ,navy designation4 ,bernard ,luskin of the ,lamont ,geological ,observatory1 in co-operation with the ,times ,facsimile ,company1 adapted the ,times ,facsimile receiver to do the timing and recording function of the echo sounder1 using a standard ,,uqn receiver and transmitter 7without recorder74 ,more than #bjj1jjj miles of ,,pdr soundings have now been obtained by expeditions of the ,lamont ,geological ,observatory4 ,the apparatus originally described by ,luskin et al4 7#aied7 has been extensively improved 7,luskin and ,israel1 #aief74 ,the ,times ,facsimile-,lamont ,,pdr performs the timing and recording functions with an accuracy of better than #a fathom in #cjjj4 ,this was a considerable improvement over older apparatus4 ,the ,,pdr generally uses multiple #djj-;fathom scales in which #djj fathoms is represented by #ah inches of record2 the paper is carried through the machines at #bd inches an hour4 ,other vertical scales 7i4 e41 #bjj1 #hjj1 #abjj7 can easily be provided1 and the paper transport can be changed by steps from #ab to #if inches per hour4 ,the laminated recording paper consists of two layers of light gray and a center layer of black4 ,the record is made by burning the upper gray layer and thus exposing the underlying dark layer4 ,the facsimile recording paper differs from the conventional echo-sounder record paper in that a greater range of shades can be reproduced4 ,several ,,pdr records are shown in the following text 7,pls4 #c1 #d1 #e1 #f1 #h1 #i1 #aj1 #ab1 #ac1 #ad1 #af1 #ag1 #ah74 ,effective study of the physiography of the deep-sea floor was made possible by introduction of the ,,pdr4 ,echo soundings obtained by the ,english in the area southwest of ,england have been used in the present study4 ,the accuracy of their equipment has not been adequately treated in the literature1 but it appears by comparison that most soundings are accurate to within at least #a per cent4 ,,part #b4 ,,physiographic ,,provinces ,,introduction ,descriptions of physical features of the earth's surface are found in the earliest-known writings4 ,however1 the systematic classification of land forms is relatively recent and followed the development of the science of physical geology4 ,the natural topographic divisions of the continents have been classified into physiographic provinces according to several similar systems 7,lobeck1 #aici2 ,fenneman1 #aich2 ,atwood1 #aidj2 and others74 ,these systems take into account form and age of the relief1 as well as the structure of the underlying rocks4 ,descriptions are usually given in terms of age1 process1 and structure1 with the ultimate aim the understanding of the origin and history of topography4 ,detailed topographic maps at #a3ej1jjj or larger are available and are used in conjunction with direct field observations4 ,more recently aerial photographs have greatly aided geomorphic studies4 ,the oceans1 in contrast1 have been subdivided by oceanographers merely into basins separated by ridges and swells4 ,this was done on the basis of widely spaced discrete soundings shown on charts rarely of larger scale than #a3aj million4 ,the basins were delimited by arbitrarily chosen and often crudely controlled isobaths4 ,the development and installation of continuously recording deep-sea echo sounders and their extensive use in the deep sea provide for the first time detailed topographic information on the deep-sea floor and thus a new basis for description and classification4 ,it is perhaps presumptuous at this time to refer to the topographic divisions of the sea floor as physiographic provinces when we have only scant information concerning the structure of each province1 the age1 the physical processes1 and1 in fact1 the details of topography4 ,therefore1 the classification described in the following pages is presented as a first attempt1 with the full knowledge that it will be modified and expanded by subsequent exploration4 ,we are only beginning to understand the structural significance of deep-sea physiographic provinces4 ,we now think that the correlation of topography and structure will be better under the sea than on land because of less vigorous erosion at depth in the sea4 ,if this is true1 deep-sea structural patterns may eventually be quite simple to map4 ,,nomenclature ,,and ,,classification ,,of ,,deep-,,sea ,,relief ,before the advent of continuously recorded echo-sounding profiles1 and their revelation of the texture of the sea-floor relief1 classification and nomenclature of submarine topography were based on broad closed isobaths4 ,we can characterize the older system as the bathymetric system of nomenclature in contrast to that employed in this paper1 which we can call a geomorphic or textural system4 ,the terms basin and deep used in the older literature are usually defined by closed #cjjj-1 #djjj-1 or #ejjj-meter contours as represented on the ,carte ,gnrale ,bathymtrique des ,ocans 7,international ,hydrographic ,bureau74 ,for many purposes this terminology is useful1 particularly in describing the habitat of a deep-sea fish or the locale of a water mass4 ,consequently some such system should be retained even though in many areas basin boundaries are difficult to define1 and regardless of the fact that many boundaries cut arbitrarily through physiographic provinces without regard for local province boundaries4 ,the ,atlantic has been subdivided by ,wst 7#aidj;b7 7,fig4 #d7 whose system is now in general use4 ,illustration3 ,,figure #d4--,major basins of the ,north ,atlantic1 after ,wst 7#aidj7 ,heavy solid lines indicate boundary formed by axis of ,mid-,atlantic ,ridge4 ,light solid lines indicate boundary formed by shelf breaks and submarine ridges4 ,dashed lines indicate arbitrary boundaries4 ,the nomenclature of deep-sea topography has been considered by several committees during the past half century4 ,the most recent recommendations published by ,wiseman and ,ovey 7#aiec2 #aiee7 are followed wherever applicable4 ,the older systems of nomenclature1 however1 are not rigidly employed since we are dealing with textural provinces based on profiles obtained with continuously recording echo sounders rather than bathymetric provinces defined by closed isobaths4 ,,units ,,of ,,depth ,,and ,,slope ,on the profiles and echograms the vertical scale is in units of echo-sounding time rather than in units of true depth4 ,in other words1 all depths are calculated under the assumption that the vertical sound velocity is #hjj fathoms per second4 ,considering that the sound travels to the bottom and back1 the calculation is based on #djj fathoms per second of lapsed time4 ,since the average vertical velocity is1 within the area covered1 always slightly less than #hjj fathoms per second1 the true depth is always slightly greater than the echo-time depth as expressed in nominal fathoms4 ,figure #e shows the range of corrections which must be applied in various parts of the area4 ,the spot depths indicated on the physiographic diagram are in units of true depth corrected according to ,matthews' tables 7#aici7 for regional variations in the average vertical sounding velocity4 ,illustration3 ,,figure #e4--,sound-velocity corrections for echo soundings ,add correction to uncorrected echo sounding to obtain true depth4 ,curves ,i and ,,ii are representative of ,north ,atlantic #ag-ej,n4 exclusive of the ,grand ,banks region4 ,curves ,,iii and ,,iv are representative of the deep-water areas near the ,grand ,banks4 ,curves are based on ,matthews 7#aici7 and are for use only where assumed sounding velocity is #hjj fathoms_/second4 ,all soundings mentioned in the text are uncorrected for sound velocity4 ,illustration3 ,,figure #f4--;,conversion diagram for degrees1 per cent grade1 feet per statute mile1 and gradient 7a7 ,values of gradient from #a3aj-a3aejj2 7b7 ,values of gradient from #a3ajj-a3ejjj ,the inclination of the bottom is given as the tangent of the angle between the sloping plane and the horizontal expressed as a ratio of integers4 ,these ratios are referred to as gradients4 ,in ,figure #f slope values expressed in degrees1 per cent grade1 feet per statute mile1 and gradient are compared4 ,with a few exceptions all profiles are represented with a #dj3a vertical exaggeration4 ,to facilitate judging the magnitude of slopes on these profiles1 ,figure #g shows various gradient ratios at a #dj3a vertical exaggeration4 ,slope corrections have not been made to the soundings4 ,except in special cases such corrections would make insignificant changes in the #dj3a profile4 ,all distances are given in nautical or geographical miles 7#a nautical mile #fjhj feet74 ,illustration3 ,,figure #g4--;,gradients from #a3e to #a3hjjj shown at a #dj3a vertical exaggeration ,most profiles reproduced in this paper are at #dj3a vertical exaggeration4 ,this template is provided to aid the reader in judging slopes on these exaggerated profiles4 ,illustration3 ,,figure #h4--,outline of submarine topography ,line #a1 first-order features of the crust2 line #b1 major topographic features of the ocean2 line #c1 categories of provinces and super-provinces2 line #d1 provinces2 line #e1 sub-provinces and other important features4 ,,continent ,,and ,,ocean ,the two first-order morphologic divisions of the earth's crust are continent and ocean4 ,the oceans can be divided into a few major divisions which are in turn subdivided into categories of physiographic provinces and then into individual provinces4 ,the area of the present study is composed of the three major divisions shown in ,figure #i3 continental margin1 ocean-basin floor1 and mid-oceanic ridge4 ,the discussion and description of the physiographic provinces of the ,north ,atlantic will follow the schematic outline shown in ,figure #h4 ,illustration3 ,,figure #i4--,major morphologic divisions3 ,north ,atlantic ,ocean ,the profile is a representative profile from ,new ,england to the ,sahara ,coast4 ,,continental ,,margin ,,definition ,,and ,,general ,,categories ,the continental margin includes those provinces of the continents and of the oceans which are associated with the boundary between these two first-order features of the earth4 ,general categories4--,in most areas three parallel categories of provinces can be distinguished in the continental margin 7,fig4 #aj74 ,the relatively flat portions of the submerged continental platform constitute category ,i4 ,these provinces are3 continental shelf1 epicontinental marginal seas 7e4 g41 ,gulf of ,maine71 and continental-margin plateaus 7e4 g41 ,blake ,plateau74 ,the provinces of category ,,ii include the continental slope1 marginal escarpments 7e4 g41 ,blake ,escarpment71 and the landward slopes of trenches4 ,these provinces mark the edge of the continental block4 ,category ,,iii includes the continental rise1 marginal trench-outer ridge1 and marginal basin-outer ridge complexes4 ,illustration3 ,,figure #aj4--,three categories of continental-margin provinces ,category ,i provinces lie on the continental block1 ,category ,,ii provinces form the side of the continental block1 and ,category ,,iii provinces are the upturned or depressed margins of the oceanic depression4 ,the most common type of continental margin is made up of continental shelf 7,i71 continental slope 7,,ii71 and continental rise 7,,iii74 7,fig4 #aj1 ,sahara and ,new ,york74 ,in areas where the continental rise is well developed it is composed of two parts1 the upper and the lower continental rise 7,fig4 #ae74 ,in some areas the lower continental rise is replaced by an outer ridge1 and the upper continental rise is replaced by a marginal basin or marginal trench4 ,these two latter types are illustrated in ,figure #aj by profiles marked ,blake ,plateau and ,puerto ,rico respectively4 ,seamounts and islands occur in all the continental-margin provinces4 99 99 99 99 99 ,category ,i provinces4--,the ocean overflows its basin onto the edge of the continents4 ,the principal physiographic province of this submerged portion of the continental platform is the continental shelf which is present off all the lands of the world4 ,the continental shelf is a smooth area with very low relief and is nearly everywhere limited to depths less than #bej fathoms4 ,the continental blocks are also flooded by epicontinental seas4 ,some of these have rough bottoms1 as the ,gulf of ,maine2 others are relatively smooth-floored4 ,marginal plateaus1 where present1 lie in depths of #ejj-abjj fathoms1 and many are nearly as smooth as the continental shelves4 ,,continental ,,shelf3 ,the continental shelf is a shallow 7averaging less than #ajj fathoms71 gently sloping 7less than #a3ajjj7 surface of low local relief 7less than #aj fathoms7 which extends from the shore line to the shelf break where the seaward gradient sharply increases to greater than #a3dj4 ,its width ranges from a few miles to more than #bjj miles4 ,continental shelves border all land areas4 ,because of their proximity to shore1 their shallow depth1 and their importance in navigation the continental shelves are now the best-known part of the oceans 7,veatch and ,smith1 #aici2 ,shepard1 #aidh74 ,the transition from the continental shelf to the continental slope is generally abrupt and is known as the shelf break4 ,this feature ranges in depth from #bj to more than #ajj fathoms and in form from a sharp edge to a rounded shoulder4 ,the change in the gradient is from less than #a3ajjj to greater than #a3dj4 ,,epicontinental ,,marginal ,,seas3 ,the epicontinental marginal seas are those shallow seas 7less than #aejj fathoms7 which lie on the continental block and can be distinguished from the continental shelves by their greater depth 7usually #ajj fathoms7 and possibly greater topographic irregularity4 ,most of them are enclosed by shallow banks 7 #ej fathoms7 of the continental shelf and by land4 ,the ,gulf of ,maine1 the ,gulf of ,st4 ,lawrence1 and the channels of the ,bahamas belong to this class4 ,,marginal ,,plateaus3 ,a marginal plateau is a shelflike feature which lies at greater depths than the continental shelf and is separated from the continental shelf by an incipient continental slope4 ,these features generally lie at depths greater than #ajj fathoms and less than #abjj fathoms4 ,they can be distinguished from epicontinental marginal seas by their lack of a seaward barrier or sill4 ,the surface of a marginal plateau is generally quite similar to the continental shelf in slope and in the frequency and magnitude of minor relief features4 ,the ,blake ,plateau is the only well-expressed representative of this morphologic type in the area of the diagram4 ,well-developed marginal plateaus are also found off the coast of southern ,argentina and east of ,new ,zealand4 99 99 99 99 99 ,category ,,ii provinces4--,the steep slopes which border the continental block are grouped into category ,,ii provinces4 ,loosely speaking1 we are referring to the continental slope but1 because of the complications imposed by such features as marginal plateaus and marginal trenches1 we distinguish three province types4 ,,continental ,,slope3 ,the continental slope is that relatively steep 7#c-f7 portion of the sea floor which lies at the seaward border of the continental shelf4 ,it typically drops from depths of #ej-ajj fathoms to depths of #gej-agej fathoms4 ,the top of the slope is usually well marked by a relatively sharp shelf break4 ,the base of the slope1 although less definite1 is generally abrupt4 ,as a basis of classification in those few areas where no abrupt change is noted1 we have set the gradient of #a3dj as the lowest gradient of the continental slope4 ,the setting up of a lower limit for the gradient marks a departure from the older usage in which the continental slope was defined as the slopes leading from the outer edge of the continental shelves down to the great depths of the ocean 7,shepard1 #aidh74 ,this older definition included the continental rise1 marginal plateaus1 and marginal escarpments4 ,the continental slopes are a world-wide phenomenon4 ,the details of their regional distribution in the ,north ,atlantic are covered in a later section4 ,,marginal ,,escarpments3 ,a marginal escarpment is a precipitous escarpment which forms the seaward slope of a marginal plateau4 ,such escarpments begin in depths of #ejj-aejj fathoms and are #ajjj to #bjjj fathoms high4 ,the base of the escarpment is well marked by an abrupt change in slope4 ,gradients of marginal escarpments exceed #a3aj4 ,the ,blake ,escarpment is a marginal escarpment4 ,similar features are found in the ,gulf of ,mexico and off the southeast coast of ,argentina4 ,,landward ,,slopes ,,of ,,trenches3 ,this term was introduced to set apart the landward slopes of marginal trenches from the usual continental slopes found off trench-less coasts4 ,these steep slopes 7 #a3dj7 drop from depths of a few hundred fathoms near a continent to a depth of a few thousand fathoms in a marginal trench4 ,in the ,north ,atlantic the one example is north of ,puerto ,rico4 ,a large part of the circumference of the ,pacific is bounded by such features4 99 99 99 99 99 ,category ,,iii provinces4--,at the base of the continental slope a gentle gradient continues to the local level of the abyssal floor4 ,this seaward gradient ranges from #a3ajj to #a3gjj and extends over a strip from a few miles to a few hundred miles in width4 ,on many topographic profiles made at right angles to the slope of the continental margin three major breaks are visible3 the shelf break1 the base of the continental slope1 and the point where the near-by level of the ocean-basin floor intersects the more steeply sloping continental margin4 ,since we have limited the continental slope to gradients greater than #a3dj1 we split off this lower portion of the continental margin into a separate province1 the continental rise4 ,in the older bathymetric classification of relief the ocean basin--continental slope boundary was along the #bjjj- or #bejj-;fathom contour1 an arbitrary division which cut across the then-unrecognized continental rise4 ,at the base of the ,blake ,escarpment lies an enclosed basin1 and north of ,puerto ,rico the sea floor drops almost directly to the floor of a marginal trench4 ,these seemingly diverse provinces of continental rise1 marginal escarpments1 enclosed marginal basins1 marginal trenches1 and outer ridges are placed in category ,,iii because of their similarity in position with respect to the continents and ocean floor and because of other similarities shown in the deeper structure of the continental rise4 ,,continental ,,rise3 ,the continental rise1 where present1 lies at the base of the continental slope4 ,gradients on the continental rise generally range from #a3ajj to #a3gjj1 while the width ranges from a few score to a few hundred miles4 ,however1 gradients as high as #a3ej are observed in segment #c of the upper continental rise1 and gradients as low as #a3bejj are locally present in segment #b of the lower continental rise 7,tables #a and #b74 ,the seaward limit of the continental rise is generally abrupt1 and at this point regional gradients decrease to less than #a3ajjj4 ,the depth on the continental rise ranges from #gej to #bhjj fathoms4 ,local relief is moderate to low1 and1 except for infrequent seamounts and fairly frequent submarine canyons1 the local relief of the continental rise rarely exceeds #bj fathoms4 ,the continental rise is well developed over most of the area covered by the physiographic diagram4 ,the major exceptions are north of the ,iberian ,peninsula where the rise is present1 but extremely narrow1 and in the southwestern third of the map in the area south of ,cape ,hatteras1 where it is not present4 ,in this latter area the geographical position usually filled by the continental rise is occupied by the low1 broad outer ridge and the enclosed marginal basin and marginal trench4 ,,outer ,,ridge3 ,an outer ridge is a broad ridge generally more than #ajj miles wide that rises from less than #ajj fathoms to about #ajjj fathoms above the adjacent floor4 ,it lies parallel to the continental margin and may enclose a basin or trench on the landward side4 ,the local relief of an outer ridge is generally a little greater than that of the continental rise but much more subdued than that on the oceanic rises and mid-oceanic ridges4 ,,marginal ,,basin3 ,a marginal basin1 where present1 lies at the foot of the continental slope or at the base of a marginal escarpment4 ,it is slightly shallower than the general level of the ocean basins and is bounded on the seaward side by an outer ridge4 ,part of its floor is generally occupied by an abyssal plain4 ,,marginal ,,trench3 ,a marginal trench is a narrow1 steep-sided feature running closely parallel to the trend of the continental margin2 it is generally at least #ajjj fathoms below the general level of the adjacent ocean floor4 ,it is separated from the ocean floor by a low outer ridge which rises #ajj-ejj fathoms above the level of the adjacent ocean floor4 ,the bottom of a trench is generally rugged except near the deepest spots where it is flat4 ,the combination of marginal basin and outer ridge replaces the continental rise east of the ,blake ,plateau4 ,north of ,puerto ,rico this combination is replaced by a marginal trench-outer ridge complex4 ,the reason for this grouping is discussed in a later section4 ,submarine canyons cut across all the continental-margin provinces except isolated portions of the outer ridge4 ,submarine canyons range from less than a mile to more than #aj miles in width and from less than #aj to nearly #ajjj fathoms in depth4 ,canyons are most abundant on the continental slope4 ,however1 a smaller number persist across the continental rise4 ,they are also found on the marginal escarpments and on the landward slopes of trenches4 ,shepard 7#aidh71 ,kuenen 7#aiej71 ,veatch and ,smith 7#aici71 ,de ,andrade 7#aicg71 ,johnson 7#aici71 and others have discussed the continental-slope canyons at great length4 ,canyons in the continental rise of the ,north ,atlantic were discovered and mapped by ,ericson1 ,ewing1 and ,heezen 7#aiea74 ,,regional ,,description ,,of ,,continental ,,margin ,this discussion is based on continuously recorded echo-sounding traverses made by ,lamont ,geological ,observatory expeditions4 ,profiles approximately perpendicular to the continental margin are reproduced in ,plates #bd and #be4 ,none is precisely perpendicular1 and thus slight distortions of slopes and widths of the features are unavoidable4 ,,eastern ,,north ,,america3 ,thirty-four profiles of the continental margin of eastern ,north ,america are presented in ,plate #bd4 ,the positions of the profiles are indicated on the index chart in ,plate #bc4 ,all profiles show the three categories of continental-margin provinces4 ,profiles ,w-#a to ,w-#ba ,plate #bd show the more general succession of shelf1 slope1 and rise1 while profiles ,w-#bb to ,w-#cd show the outer ridge-marginal basin and outer ridge-marginal trench complexes4 ,each of the #cd profiles exhibits a continental shelf although it may range from #bj to #cjj miles in width4 ,on each a shelf break is present at depths of #bj-aej fathoms4 ,each profile shows a continental slope1 the base of which may be from #cjj to #aijj fathoms deep4 ,northern ,grand ,banks ,sector4--,on profiles ,w-#a to ,w-#f 7,pl4 #bd71 across the ,grand ,banks of ,newfoundland1 the shelf ranges from #abj to #bhe miles in width4 ,exceptionally strong local relief of #ej-ajj fathoms is found on the shelf in profile ,w-#a northeastward from ,newfoundland4 ,the shelf break1 which occurs at #aej fathoms1 is abnormally deep--more than twice the depths found off ,new ,england4 ,the continental slope has a typical gradient of #a3bj but is unusually short as the continental rise is reached at #gbe fathoms4 ,from this depth the continental rise descends to the #agjj-;fathom curve at a gradient of #a3adj4 ,this gentle slope is interrupted by a group of exceptionally rugged lower continental rise hills which rise to #abej fathoms4 ,northeast of the hills the #bbjj-;fathom line marks the rather abrupt beginning of the abyssal plain which slopes seaward at a gradient of #a3aajj4 ,flemish ,cap4--,profile ,w-#b crosses the ,grand ,banks1 along its widest east-west axis1 and also the semidetached bank called ,flemish ,cap4 ,the shelf is much smoother than in profile ,w-#a1 except for a small deep of about #ajj fathoms immediately east of ,newfoundland4 ,the shelf break at #aej fathoms is followed by a continental slope #aej to #ejj fathoms deep which has a gradient of #a3bj4 ,the ,flemish ,cap is a difficult feature to classify4 ,it is too large to be a seamount and too shallow to be a marginal plateau4 ,we must treat it as a part of the continental shelf1 semidetached from the rest by a #fej-;fathom-deep channel4 ,the eastern flank of the ,flemish ,cap slopes off at gradients of #a3ajj and #a3fj until at a depth of #fej fathoms the bottom drops precipitously to #agej fathoms at a gradient of #a3aj4 ,seaward of this point an #he-mile-wide continental rise has a gradient of #a3fe and #a3bej down to the ,newfoundland ,abyssal ,plain which is at a depth of #bdjj fathoms4 ,twenty miles east of the continental rise this profile crosses the ,northwest ,atlantic ,mid-,ocean ,canyon4 ,on profile ,w-#c the shelf is quite smooth1 and the shelf break is reached at #fj fathoms4 ,the profile runs slightly oblique to the continental slope and reveals a series of submarine canyons4 ,the base of the slope is at #agjj fathoms where the gradient drops to less than #a3bjj4 ,illustration3 ,,figure #aa4--,two east-west profiles of ,southeast ,newfoundland ,ridge ,positions of profiles are indexed on ,plate #bc4 ,both profiles plotted from nonprecision soundings 7,,nmc74 ,southeast ,newfoundland ,ridge4--,from the southern tip of the ,grand ,banks a broad ridge runs southeasterly toward the ,mid-,atlantic ,ridge and forms a natural barrier between the ,newfoundland ,basin and the ,north ,america ,basin to the south4 ,since it is almost impossible to define a boundary between the continental rise and the ridge1 we consider the ,southeast ,newfoundland ,ridge an extension of the continental rise4 ,the ridge is #fj-ajj miles wide1 and its crest plunges southeastward from depths of #aejj fathoms near #ej ,w4 to depths of #bbjj fathoms near #de ,w4 ,profiles ,n-#a and ,n-#b 7,fig4 #aa7 cross the ,southeast ,newfoundland ,ridge at about #da4e ,n4 and #ci4e ,n4 respectively4 ,profile ,n-#a is of poor quality1 which probably accounts for the lack of fine-textured relief4 ,the ,mid-,ocean ,canyon is again seen at the eastern end of ,profile ,n-#b4 ,profile ,w-#e 7,pl4 #bd7 crosses the ,southeast ,newfoundland ,ridge from north to south4 ,the similarity of profiles ,w-#e and ,w-#bc suggests that the ,southeast ,newfoundland ,ridge is an outer ridge of the same kind as the one east of the ,blake-,bahama region4 ,the northern one is not so long1 and it does not totally enclose a basin4 ,otherwise1 it is quite similar to the outer ridge east of the ,bahamas in relative position1 size1 and surface features4 ,the term ,southeast ,newfoundland ,ridge was proposed by ,wst 7#aidj;b2 #aidc7 and the feature has been shown on bathymetric charts 7,tolstoy1 #aiea7 and profiles 7,emery1 #aiej74 ,this ridge will be discussed again in connection with the ,mid-,ocean ,canyon and the ocean-basin floor4 ,southern ,grand ,banks ,sector4--,profiles ,w-#d and ,w-#e cross the southern tip of the ,grand ,banks4 ,the shelf break is at #ej fathoms on both profiles4 ,on ,profile ,w-#d an apparent gradient of #a3be extends from #bjj to about #ajjj fathoms where1 after some irregularities probably associated with submarine canyons1 the gradient drops to #a3dj4 ,this lower gradient extends to #agej fathoms4 ,profile ,w-#e is quite similar to ,w-#d except that a steep initial slope of #a3e1 from about #bjj fathoms to #fej fathoms1 is followed by a gradient of #a3hj which continues to #ajjj fathoms4 ,this same terracelike feature is also seen on ,w-#c1 ,w-#d1 ,w-#e1 ,w-#f1 ,w-#g1 and ,w-#h4 ,below #ajjj fathoms a gradient of about #a3ej is found on profiles ,w-#d1 ,w-#e1 ,w-#f1 ,w-#g1 and ,w-#h4 ,profile ,w-#f runs south of the ,grand ,banks through the epicenter of the #aibi ,grand ,banks earthquake and then south through the area passed over by the #aibi ,grand ,banks turbidity current 7,heezen and ,ewing1 #aieb74 ,the depression marked by the #aaej-;fathom sounding on the continental slope in ,profile ,w-#f is a canyon running south from the ,laurentian ,channel4 ,the continental rise is #bej miles wide and has an average gradient of #a3djj over its deepest third4 ,at a depth of #bgej fathoms the gradient abruptly drops to #a3bjjj1 and this marks the northern edge of the ,sohm ,abyssal ,plain4 ,illustration3 ,,figure #ab4--,laurentian ,channel ,profile replotted from ,,nmc echogram ,illustration3 ,,figure #ac4--;,eastern ,channel1 ,gulf of ,maine ,profile replotted from ,,nmc echogram ,laurentian ,channel4--,between ,nova ,scotia and ,newfoundland a #fj-mile-wide1 steep-sided1 flat-floored channel cuts across the continental shelf connecting the ,gulf of ,st4 ,lawrence and the open ocean4 ,the nearly flat1 smooth floor of this channel lies at about #bcj fathoms depth4 ,figure #ab shows a cross-section of the ,laurentian ,channel near its seaward end4 ,the origin and physiography of the channel has been treated by ,shepard 7#aica2 #aidh72 its structure has been reported by ,press and ,beckmann 7#aied74 ,the ,laurentian ,channel continues as a steep-sided1 box-shaped feature for more than #ejj miles into the ,gulf of ,st4 ,lawrence4 ,scotian ,shelf ,sector4--,the term ,scotian ,shelf was introduced by ,canadian oceanographers and refers to the continental shelf southeast of ,nova ,scotia from the ,laurentian ,channel to the ,gulf of ,maine4 ,this region is illustrated by ,profiles ,w-#g1 ,w-#h1 ,w-#i1 ,w-#aj1 and ,w-#aa which run at slightly different directions1 all starting in the vicinity of ,halifax1 ,nova ,scotia4 ,along the entire ,scotian ,shelf a series of #abj-;fathom depressions are located #aj to #hj miles off shore4 ,a nearly continuous bank #bj-fj fathoms deep and #aj-be miles wide lies along the seaward edge of the ,scotian ,shelf4 ,from northeast to southwest this feature is divided by low saddles into ,banquereau ,bank 7#bj-dj fathoms71 ,sable ,island ,bank 7#j-bj fathoms71 ,emerald ,bank 7#dj-fj fathoms71 ,lahave ,bank 7#ej-fj fathoms71 and ,browns ,bank 7#bj-fj fathoms74 ,these shelf-edge banks culminate in the low1 sandy ,sable ,island which stretches for about #be miles along the outer edge of the shelf4 ,in profile ,w-#g the break from the nearly flat shelf to a gradient of #a3ej occurs at #ej fathoms2 a second break occurs at #hj fathoms4 ,a gradient of #a3aj is reached at the #aej-;fathom curve4 ,profile ,w-#aa is somewhat similar to ,w-#g in the form of the shelf break4 ,profiles ,w-#h1 ,w-#i1 and ,w-#aj show shelf breaks at #ej1 #fj1 and #gj fathoms respectively4 ,the gradient of the continental slope off the ,scotian ,shelf ranges from #a3aj to #a3be along the profiles4 ,in profiles ,w-#g1 ,w-#h1 ,w-#aj1 and ,w-#aa the #a3be gradient abruptly decreases to #a3gj at about #gjj fathoms2 in ,w-#i the #a3be gradient continues to almost #bjjj fathoms4 ,it is difficult to decide whether to include the #a3dj to #a3fj segments with the continental slope or with the continental rise4 ,however1 since we have picked the gradient of #a3dj as the minimum gradient for true continental slopes1 these segments fall within the continental rise4 ,the continental rise thus defined averages #afj miles in width off the ,scotian ,shelf4 ,gradients are generally greater here than in the continental rise farther south4 ,the ,gully1 a large submarine canyon shown on navigational charts1 lies about #be miles east of ,sable ,island4 ,the submarine canyons of the ,scotian ,shelf have not been accurately mapped1 but the existence of many canyons in this area has been shown by several fathograms obtained in this vicinity4 ,figure #ad illustrates one sounding profile nearly parallel to the shelf near the ,gully4 ,several small canyons about #ajj fathoms deep occur between #ajj and #gjj fathoms4 ,several larger canyons #cjj-ejj fathoms deep and #g-aj miles wide are crossed on the lower continental slope and upper continental rise4 ,illustration3 ,,figure #ad4--,submarine canyons off the ,scotian ,shelf ,profile replotted from ,,nmc echogram runs nearly parallel to trend of continental slope near ,sable ,island4 ,on navigational charts largest canyon is known as the ,gully4 ,gulf of ,maine ,entrance4--,southwest of the ,scotian ,shelf there is a narrow gap in the continental shelf similar to the ,laurentian ,channel4 ,this feature1 called either the ,northeast ,trough 7,shepard1 #aidh7 or ,eastern ,channel of the ,gulf of ,maine1 is #ae miles wide and about #aej fathoms deep2 it provides a deep-water entrance to the ,gulf of ,maine 7,fig4 #ac74 ,the ,gulf of ,maine is enclosed by ,georges ,bank off the ,new ,england shelf1 ,cape ,cod1 and southern ,nova ,scotia4 ,this entrance has recently been described by ,torphy and ,zeigler 7#aieg74 ,gulf of ,maine ,interior4--,much of the interior of the ,gulf of ,maine has been surveyed in exceptional detail by the ,coast and ,geodetic ,survey4 ,the reader is referred to ,murray's paper 7#aidg7 for a thorough description of the floor of the ,gulf of ,maine4 ,in general the floor is extremely irregular with several #bj- to #dj-;fathom hills per mile4 ,the floor is covered by sediment which transmits sound so readily that the area is noted for exceptionally pronounced sub-bottom reflections from the rock layers beneath the sediment4 ,northeastern ,united ,states ,sector4--,from the northeast tip of ,georges ,bank to ,cape ,hatteras the continental margin is remarkably uniform in morphologic detail4 ,profiles ,w-#ab to ,w-#ai differ very little from the type profile off northeastern ,united ,states 7,fig4 #ae74 ,the continental shelf and slope in this area are better surveyed than in any other area in the ,atlantic4 ,the surveys of the ,coast and ,geodetic ,survey were contoured and described by ,veatch and ,smith 7#aici74 ,the sediment studies of ,stetson 7#aicf2 #aich2 #aidi7 and the seismic studies of ,ewing and others 7#aicg et seq47 make this geologically the best-known shelf and slope in the world4 ,many large and well-mapped canyons cut the continental slope from ,georges ,bank to ,cape ,hatteras4 ,the large submarine canyons off ,georges ,bank have attracted great interest because of their remoteness from rivers and associated discharges of river sediments4 ,the continental shelf is #ej to #ajj miles wide in this sector4 ,toward ,cape ,hatteras the coastal plain widens as the shelf narrows4 ,the combined features are called the emerged and submerged coastal plain4 ,the gradient of the continental slope ranges from #a3h to #a3ae and the base of the slope with one exception is at #aaej #ajj fathoms4 ,the shelf break is at about #ej fathoms on all profiles4 ,on profiles ,w-#ab1 ,w-#ac1 ,w-#ad1 ,w-#ae1 ,w-#ah1 and ,figure #a of ,plate #d there is a second break at #ge-ajj fathoms4 ,the break between the continental slope and the upper continental rise is abrupt at some places and occupies a distance of #e to #aj miles in other places 7,fig4 #af74 ,in each case the gradient of the next lower #cj- to #ej-mile segment is #a3ajj4 ,all profiles from ,georges ,bank to ,cape ,hatteras1 a span of more than #ejj miles1 show both an upper and a lower continental rise 7,profiles ,w-#ac1 ,w-#ai1 and ,fig4 #ae74 ,the uniformity in the continental slope gradient carries over into the continental rise4 ,both the upper continental rise and the lower continental rise are divided into three segments4 ,the width1 gradient1 and depths of each of the slope segments are remarkably similar4 ,representative values based on profiles ,w-#ac to ,w-#ai and ,figure #ae are shown in ,table #a4 ,illustration3 ,,figure #ae4--;,continental margin provinces3 ,type profile off northeastern ,united ,states4 ,profile plotted from ,,pdr records4 ,this profile is representative of the sector from ,georges ,bank to ,cape ,hatteras4 ,,table #a4--;,characteristics of the continental rise1 northeastern ,united ,states sector3 representative values of gradient1 depth1 and width of slope segments ,values measured from profiles ,w-#ac to ,w-#ai ,depth ,segment ,upper ,lower ,gradient ,width edge edge ,upper continental rise #a #aaej #aej #adej #bjj #a3ajj #bj #cj #e #b #adej #bjj #afej #aej #a3bge #be #dj #ae #c #afej #aej #baej #bjj #a3ij #cj #cj #ae ,lower continental rise #a #baej #bjj #bcej #ajj #a3bej #ej #dj #aj #b #bcej #ajj #bcej #ajj #a3adjj #ajjj #ej #bj #c #bcej #ajj #bgbe #ajj #a3aej #cj #fj #bj ---------------------------------------- ------------------ ,the upper continental rise and the lower continental rise are essentially terrace or shelflike features4 ,each has a relatively steep 7#a3ej-a3bjj7 outer face 7segment #c7 and a relatively gentle 7#a3bej-a3bjjj7 shelflike surface 7segment #b74 ,in each case a slope of intermediate gradient 7#a3hj-a3cjj7 7segment #a7 connects the upper shelflike surface with the next higher face4 ,in the case of the upper continental rise the next higher face is the continental slope4 ,other smaller-scale terracelike features may eventually be correlated along the strike when more data are available4 ,the local relief exceeds #bj fathoms in the deeper parts of segment #c of the lower continental rise4 ,a range of hills extends for a few hundred miles along the base of the continental rise as indicated on the physiographic province chart 7,pl4 #bj74 ,these hills1 known as the lower continental rise hills1 are #cj-ajj fathoms high and each is #a to #c miles wide4 ,an echogram 7,pl4 #c1 fig4 #d7 shows three continental rise hills4 ,the only other part of the continental rise where relief of more than #bj fathoms is generally encountered is in segment #a of the upper continental rise4 ,the irregularity in this case is probably related to the extensions of numerous continental-slope canyons onto the continental rise4 ,relief of #e-aj fathoms is almost universal in segments #a and #b of the upper continental rise4 ,the echogram reproduced in ,figure #a of ,plate #c shows typical minor-relief features of the upper continental rise4 ,an oblique crossing of a submarine canyon on the upper continental rise is shown in ,figure #b of ,plate #c4 ,the smooth topography typical of most of the remainder of the continental rise is well illustrated by the echogram shown in ,figure #c of ,plate #c4 ,the ,hudson ,submarine ,canyon cuts across the continental rise in this sector4 ,a chart contoured by ,ivan ,tolstoy and the authors from surveys made in #aidi is shown in ,plate #b 7,ericson1 ,ewing1 and ,heezen1 #aiea74 ,a series of #cj cross profiles is shown in ,figure #ag4 ,illustration3 ,,figure #af4--,tracings of ,,pdr records of continental and insular slopes 7a74 ,insular slope of ,madeira southwest of ,funchal4 7b74 ,continental slope of ,europe4 7c74 ,continental slope off northeastern ,united ,states4 ,the ,hudson ,canyon1 which is more than #ejj fathoms deep and #e miles wide in the continental slope 7,upper ,gorge71 narrows to less than #b miles and shallows to #ej fathoms at the base of the continental slope4 ,as it cuts across segment #b of the upper continental rise the canyon gradually deepens4 ,when it cuts into the upper part of segment #c the canyon deepens to #cjj fathoms1 widens to #c miles1 and forms the ,lower ,gorge4 ,the canyon gradually narrows and shallows as it cuts across the lower continental rise4 ,it ends near ,caryn ,peak where sediment cores indicate an extensive delta or submarine alluvial cone4 ,the upper continental rise and the lower continental rise can be tentatively traced northeastward through the ,scotian ,shelf and ,grand ,banks sectors4 ,the irregular bench at #bbej-bdej fathoms on ,w-#f and the bench at #bcjj fathoms on ,w-#h and ,w-#aa can probably be referred to segment #b of the lower continental rise4 ,illustration ,near ,cape ,hatteras the entire character of the continental margin changes4 ,benches which were barely discernible farther north widen to form a series of broad steps which resemble a giant staircase descending to the depths of the ,atlantic4 ,these benches appear to merge with the benches of the ,blake ,plateau and ,escarpment farther south4 ,however1 insufficient profiles exist to permit a firm correlation4 ,illustration3 ,,figure #ag4--;,cross sections of ,hudson ,submarine ,canyon ,replotted from nonprecision soundings 7,,nmc7 made #aidi-aiej ,blake ,plateau ,sector4--,this sector is divided into two parts1 the northern part from ,cape ,hatteras to #bi ,n4 7essentially a transition zone7 and the southern or main ,blake ,plateau between #bi ,n4 and the northern edge of the ,bahamas at #bf ,n4 ,the shelf break lies parallel to the coast1 about #fj miles offshore1 from just south of ,cape ,hatteras to ,cape ,canaveral4 ,the continental slope extends 7at a gradient of #a3dj7 only to depths of #cjj-djj fathoms where the lower gradients 7ca4 #a3ajjj7 of the ,blake ,plateau are found4 ,the main or southern ,blake ,plateau is #agj miles wide 7east-west7 and extends from the latitude of ,grand ,bahama ,island to #cj ,n4 ,from this point to ,cape ,hatteras the ,blake ,plateau narrows and disappears4 ,the ,blake ,escarpment forms a precipitous drop to abyssal depths along the eastern edge of the plateau4 ,the top of the ,blake ,escarpment lies at about #eej fathoms1 and its base at about #bfjj fathoms4 ,the ,escarpment is typically formed by two or three distinct slope segments4 ,an echogram obtained along a track running southeast from ,charleston1 ,south ,carolina1 is reproduced in ,figure #a of ,plate #g4 ,the continental shelf extends from the shore at an extremely low gradient to the #be-;fathom isobath where a small definite notch marks an increase in gradient to #a3ajjj4 ,this gradient continues to the #ej-;fathom isobath where it changes to #a3dj4 ,at the #ij-;fathom curve the gradient increases to #a3abj and continues to #afj fathoms where it finally increases to #a3dj4 ,this continental slope drops from #afj fathoms to #bhj fathoms where the gradient flattens1 and the surface changes from smooth to rough1 with hills #aj to #bj fathoms high and half a mile to #a- miles wide4 ,these hills1 which extend for #d-f miles along the profile1 directly underlie the ,gulf ,stream4 ,for #ej miles seaward of these hills the ocean floor is irregular between #bcj and #cjj fathoms4 ,at #ij miles from shore five eastward-facing scarps #aj-bj fathoms high form a striking contrast to the generally smooth1 gently rolling topography4 ,at #cjj fathoms the gradient increases to #a3bjj1 and the sea floor drops for the next #bd miles to #djj fathoms where a few small hills are associated with a drop in the gradient to #a3ajjj4 ,southeast of this point the bottom is smooth until at a depth of #dcj fathoms a steep scarp drops abruptly #cj fathoms to form a mile-wide depression #bj-cj fathoms deep4 ,the southeast side of this feature rises to #dde fathoms1 and southeastward of a few #e-;fathom scarps the surface of the ,blake ,plateau becomes smooth4 ,illustration3 ,,pl4 #c ,,figure #a4 ,,upper ,,continental ,,rise ,,figure #b4 ,,oblique ,,crossing ,,of ,,submarine ,,canyon ,,figure #c4 ,,smooth ,,bottom ,,of ,,lower ,,continental ,,rise ,,figure #d4 ,,lower ,,continental ,,hills ,,representative ,,pdr ,,records ,,from ,,continental ,,rise ,,of ,,northeastern ,,united ,,states ,illustration3 ,,pl4 #d ,,figure #a4 ,,shelf ,,break ,,and ,,continental ,,slope ,,off ,,new ,,york ,,figure #b4 ,,small ,,hills ,,on ,,continental ,,slope ,,off ,,daytona ,,beach1 ,,florida ,,figure #c4 ,,small ,,hills ,,in ,,the ,,straits ,,of ,,florida ,,figure #d4 ,,small ,,abrupt ,,depressions ,,on ,,the ,,inner ,,part ,,of ,,the ,,blake ,,plateau ,,pdr ,,records ,,from ,,continental ,,slope ,,and ,,blake ,,plateau ,the positions of all echo-sounding records are shown in ,plate #cj4 ,depth in fathoms4 ,illustration3 ,,pl4 #e ,,figure #a4 ,,west ,,of ,,the ,,crest ,,of ,,the ,,outer ,,ridge ,,figure #b4 ,,western ,,side ,,of ,,outer ,,ridge ,,near ,,abyssal ,,plain ,,figure #c4 ,,blake-,,bahama ,,abyssal ,,plain ,,pdr ,,records ,,from ,,outer ,,ridge ,,east ,,of ,,the ,,blake ,,plateau ,,and ,,from ,,the ,,blake-,,bahama ,,abyssal ,,plain ,depth in fathoms3 ,the outgoing pings as well as scattering layers are recorded in the #j-djj fathom scale range2 the bottom topography may lie within the range of any multiple of #djj fathoms4 ,the depth scales indicated on the plates refer to the profiles of bottom topography4 ,for example--,figure #a of ,plate #e shows a #cjj fathom deep scattering layer over which the bottom profile has been superimposed4 ,illustration3 ,heezen et al41 ,,pl4 #f ,,pdr ,,record ,,of ,,outer ,,ridge ,,showing ,,sub-,,bottom ,,horizon ,one #c millisecond ping was transmitted and received once each second4 ,depth in fathoms4 ,the same general succession of topographic features is shown in a echogram 7,pl4 #g1 fig4 #b7 taken along a southeast-northwest line east of ,daytona ,beach1 ,florida4 ,the small definite notch at #bf fathoms is present1 but a significant difference between the two echograms is seen between #ij and #cjj fathoms4 ,on the ,charleston profile a steep #a3dj gradient slope marks this depth range1 while1 on the ,daytona ,beach profile1 the gradient is relatively gentle 7#a3ahj72 small but probably significant benches are found at #bbe1 #bgj1 #bij1 #cge1 and #che fathoms4 ,both profiles have the same characteristic rugged #e- to #ae-;fathom hills at #djj fathoms at a point underlying the ,gulf ,stream4 ,on the ,charleston profile a broad1 gently fractured arch separates the continental slope from the smooth outer part of the ,blake ,plateau4 ,the small1 sharp-crested hills noted on the ,daytona ,beach and ,charleston profiles are also found at the north end of the ,straits of ,florida 7,pl4 #d1 fig4 #b74 ,blake ,escarpment4--,profiles ,w-#bc1 ,w-#bd1 and ,w-#be and ,figure #ah illustrate the form of the ,blake ,escarpment4 ,the outer edge of the ,blake ,plateau abruptly breaks off at about #fjj fathoms4 ,here gradients increase to #a3cj4 ,this segment continues with a few minor breaks to a depth of #abjj to #aejj fathoms where a narrow bench or at least a major break in slope occurs4 ,below this bench the escarpment drops so steeply that only a few side echoes are recorded4 ,the gradient here exceeds #a3b in several profiles4 ,at #bdjj fathoms there is in places another narrow bench1 but on other profiles the abyssal plain of the floor of the ,blake-,bahama ,basin lies directly at the foot of the steepest segment4 ,a peculiar fact is that along many east-west cross sections the deepest point in the basin lies directly at the foot of the escarpment4 ,a similar deepening adjacent to the ,campeche and ,west ,florida escarpments in the ,gulf of ,mexico has been reported 7,ewing1 ,ericson1 ,heezen1 #aieh74 ,antilles ,outer ,ridge4--,south of ,cape ,hatteras a ridge ranging in width from #fj to #bjj miles lies about #ajj miles east of the ,blake ,escarpment and the ,bahama ,banks4 ,the ridge has two parallel crests #ajj miles apart which both plunge to the south4 ,at #cj,n4 the crests average about #afjj fathoms in depth1 but at #be,n4 they are #bgej fathoms1 a drop of nearly #ajjj fathoms in #cjj miles4 ,the smooth rolling topography of the ridge between ,cape ,hatteras and #bd,n4 resembles the continental rise off ,new ,york or1 in some areas1 the somewhat stronger relief of the ,bermuda ,plateau of the central ,bermuda ,rise 7,pl4 #e1 figs4 #a1 #b74 ,south of #bd,n4 and in the vicinity of ,hispaniola the ridge is poorly known and difficult to study because of its low relief and the large errors in most nonprecision soundings taken in such a great depth of water4 ,north of ,puerto ,rico the outer ridge appears as a clearly defined feature between the ,puerto ,rico ,trench on the south and the ,nares ,abyssal ,plain on the north4 ,again there are two parallel crests #fj miles apart marked by low relief of #bj to #ajj fathoms at a depth of #bgej fathoms4 ,the ,antilles ,outer ,ridge1 continuing to the east1 merges with the ,lower ,step of the ,mid-,atlantic ,ridge4 ,but more probably it skirts the ,lesser ,antilles to join the continental rise off ,south ,america4 ,the crest zone is covered by ,globigerina ooze in the north and red clay in the south2 it is isolated from the silty clays of the continental slope except on its northwest flank4 ,sub-bottom echoes appear on fathograms taken across the outer ridge4 ,data suggest that a prominent #h- to #aj-;fathom sub-bottom interface extends over the outer ridge between ,san ,salvador and #cj,n4 7,pl4 #f74 ,bahamas ,sector4--,the ,bahamas sector can be divided into two parts3 7#a7 the broad 7#bjj miles wide7 northern area dominated by broad1 shallow banks broken by relatively narrow1 deep 7ca4 #ajjj fathoms7 tongues or channels2 7#b7 the narrow southeastern part where the banks decrease in area and the tongues deepen 7to #bbjj fathoms7 and widen4 ,this southeastern part tapers to the east in the direction of the ,puerto ,rico ,trench4 ,the southeast tip of this area is formed by ,navidad ,bank1 whose eastern slopes drop to the floor of the ,puerto ,rico ,trench4 ,illustration3 ,,figure #ah4--,tracing of ,,pdr record of ,blake ,escarpment ,no soundings were recorded between #afjj and #bdjj fathoms1 a common difficulty on this precipitous escarpment4 ,note how ,blake-,bahama ,abyssal ,plain slopes toward the base of the escarpment4 ,illustration ,the ,bahama ,banks appear to consist of a slab superimposed on the same surface which forms the ,blake ,plateau4 ,the ,blake ,escarpment merges with the lower part of the eastern slope of the ,bahamas4 ,the slopes of the ,bahamas are precipitous2 gradients are of the order of #a3d to #a3h4 ,vertical cliffs1 which lie just below the #ej-;fathom curve1 have been reported by lead soundings 7,armstrong1 #aiec74 ,the ,tongue of the ,ocean and the ,northeast and ,northwest ,providence channels form a network of submarine canyons 7,hess1 #aicc74 ,the floor of this canyon system has a continuous down-slope gradient to the floor of the ,blake-,bahama ,basin4 ,sediment cores from the floor of the ,blake-,bahama ,basin 7#bebe fathoms7 7,ericson1 ,ewing1 and ,heezen1 #aieb7 contained thick 7#a-c m7 beds of graded calcareous sand4 ,the steep slopes of the ,bahamas are generally rocky1 and cores here reveal a variety of ,tertiary and ,cretaceous sediments4 ,exuma ,sound also is linked by submarine canyons to the ,blake-,bahama ,basin4 ,the graded calcareous sands of the ,blake-,bahama ,basin were probably carried through this submarine canyon system by turbidity currents4 ,the topographic benches of ,exuma ,sound have been described by ,lee 7#aiea74 ,the southeastern ,bahamas from ,great ,inagua to ,navidad ,bank consist of more numerous isolated banks and greater expanses of ocean floor in the depth range of #agjj-bdjj fathoms4 ,the basins behind the southern ,bahamas lie below the sill depth between the line of banks4 ,thus an abyssal plain lies entrapped in the ,hispaniola-,caicos ,channel and the southeastern portion of the ,old ,bahama ,channel4 ,profile ,w-#bi 7,pl4 #bd7 shows much irregular relief between #ajjj and #aejj fathoms4 ,puerto ,rico ,trench ,sector4--,with the disappearance of the ,bahama ,banks at the eastern edge of ,navidad ,bank1 the continental margin assumes its third mode of expression3 the marginal trench-outer ridge complex4 ,the outer ridge1 which nearly disappeared in the southeastern ,bahama sector1 again becomes a prominent feature4 ,the last traces of the marginal plateau merge with the continental slope of ,hispaniola and ,puerto ,rico4 ,the ,puerto ,rico ,trench develops rapidly east of ,navidad ,bank2 it lies between the outer ridge and the continental slope or landward trench slope of the ,greater ,antilles4 ,the relief of the outer ridge is somewhat greater than that observed on the outer ridge farther northwest near the ,blake ,plateau4 ,the floor of the ,puerto ,rico ,trench is divided into two parts by a longitudinal ridge4 ,the deepest parts of both are floored by nearly level trench plains4 ,the deeper one on the outer or northern side maintains a nearly constant depth at #dceh fathoms 7#dehe fathoms corrected7 for #aej miles 7,ewing and ,heezen1 #aiee74 ,the southern or inner trench is more variable in depth1 and the trench plain lies intermittently along its length4 ,its depth ranges from #cfjj to #dcjj fathoms 7uncorrected74 ,the walls of the ,puerto ,rico ,trench are formed by a series of extremely steep segments which show a remarkable persistence along the trench4 ,profiles ,w-#cb and ,w-#cc illustrate the typical trench profile north of ,puerto ,rico4 ,breaks in slope are observed at #gjj fathoms and at #aejj fathoms2 at #bjjj fathoms the gradient steepens to #a3f4 ,in this region all soundings are side echoes4 ,the outer or seaward wall of the trench is also characterized by a succession of laterally persistent slope segments4 ,a bench at #chjj fathoms at the top of a scarp which drops to the bottom of the trench is characteristic of several profiles4 ,anegada ,passage4--,the ,virgin ,islands ,bank extends #cj miles east of ,puerto ,rico along the south side of the ,puerto ,rico ,trench4 ,between the ,virgin ,islands ,bank and ,st4 ,croix a deep passage cuts through from the ,atlantic to the ,caribbean4 ,this deep passage is #acj miles long and runs along an e-ne-w-sw line4 ,its walls are extremely steep 7#i-dc7 7,frassetto and ,northrop1 #aieg74 ,the structure of this feature has been studied by ,shurbet and ,worzel 7#aieg7 and by ,j4 ,ewing et al4 7#aieg74 ,,southwestern ,,europe ,,and ,,northwest ,,africa3 ,the continental margin of ,europe and ,africa is illustrated in ,plate #be by only #bc profiles1 and therefore our description of this area cannot be as detailed as that for ,north ,america4 ,for purposes of description we have broken the area into four sectors of contrasting type3 7#a7 the ,anglo-,french sector3 7#b7 the ,iberian sector2 7#c7 the ,gibraltar sector2 and 7#d7 the ,north ,african sector4 ,in all but the three profiles in the ,gibraltar sector there is a well-defined continental shelf4 ,the continental slope is everywhere present but ranges widely in height and gradient4 ,the continental rise is extremely well developed off ,africa but virtually absent in the ,bay of ,biscay4 ,abyssal plains are shown on almost every profile1 but their depth ranges from #beej to #cjge fathoms1 and their width from #ej to #bej miles4 ,anglo ,french ,sector4--,profiles ,e-#a1 ,e-#b1 and ,e-#c are representative of the ,anglo-,french sector which extends from #de ,n4 to #fj ,n4 ,only the southern part of this sector is shown on the physiographic diagram4 ,the continental slope is broken by a prominent bench or marginal plateau at #ajjj-abjj fathoms4 ,the northwest corner of the physiographic diagram south to #db ,n4 is included in ,hill's 7#aief7 contour chart4 ,according to this chart the prominent #abjj-;fathom bench extends for more than #ijj miles along the continental margin from #de to #fj ,north ,latitude4 ,the continental slope from the shelf break to the prominent bench exhibits smaller benches and changes in slope1 many of which probably will be correlatable when more profiles are obtained in this region4 ,the general gradient of this portion of the slope ranges from #a3aj to #a3cj4 ,on the bench individual slope segments range from #a3dj to #a3hj4 ,below the bench the sea floor drops from #aejj to #bajj fathoms at gradients of #a3ae to #a3cj4 ,in profiles ,e-#a and ,e-#c a narrow continental rise about #gj miles wide with gradients of #a3bej to #a3hjj lies at the foot of the continental slope4 ,this narrow continental rise 7,pl4 #h1 fig4 #a7 gives away to a #fj-mile-wide abyssal plain at about #bejj fathoms depth 7,pl4 #h1 fig4 #c74 ,abyssal-plain gradients are about #a3bjjj in this region4 ,toward the southeast corner of the ,bay of ,biscay the #ajjj- to #abjj-;fathom bench disappears 7,fig4 #af;b72 the continental rise and continental shelf narrow to #cj miles4 ,we have only two profiles off the north coast of ,iberia1 but ,hill's 7#aief7 chart suggests that the slope is relatively steep with some prominent benches1 and that the continental shelf and continental rise narrow to #aj to #ae miles in width4 ,the prominent ,cape ,breton ,submarine ,canyon lies at the southeast corner of the ,bay of ,biscay 7,bourcart1 #aidi74 ,iberian ,sector4--,this sector was described by ,de ,andrade 7#aicg7 on the basis of a large number of discrete soundings by the ,portuguese ,hydrographic ,service4 ,relatively few echo-sounding profiles are available for the area1 and little more can be added to ,de ,andrade's description4 ,the shelf in most places is less than #bj miles in width4 ,the few echo-sounding profiles available indicate several prominent benches on the continental slope4 ,exceptionally large submarine canyons occur off ,cape ,st4 ,vincent1 ,setbal1 ,lisbon 7#b71 and ,nazar4 ,preliminary investigations by the ,lamont ,geological ,observatory indicate that ,tertiary sediments outcrop on the walls of ,lisbon and ,setbal canyons 7,sutton et al41 #aieg74 ,tertiary sediments have also been obtained by dredging and cable grappling along the continental slope of northwest ,iberia 7,wiseman and ,ovey1 #aiej74 ,gibraltar ,sector4--,the continental margin in this sector is unique4 ,the straits cut through at about #bjj fathoms so that profiles through the straits show no continental shelf4 ,a typical abrupt continental slope is also absent since only locally do slope segments have gradients exceeding #a3de4 ,a series of prominent benches is seen in the sector from profile ,e-#g to ,e-#aj4 ,the dominant bench levels in this sector are #cjj1 #fjj1 #hej1 #acjj1 #agjj1 and #bajj fathoms4 ,insufficient profiles and dredgings are available in this area to permit the correlation and dating of these benches4 ,photographs in the area show sandy and rocky bottom1 and thus dredging in this area might yield rich rewards in ancient sediments4 ,the benches are so prominent that a detailed study of the topography should be equally rewarding4 ,of particular interest is the manner in which the broad benches in the ,gibraltar area merge with the smaller benches and breaks in slope of the steep continental slopes of ,portugal and ,algeria4 ,the topography in this sector most closely resembles that of the northern ,blake ,plateau 7profiles ,w-#ba1 ,w-#bb7 and the northern part of the ,anglo-,french sector4 ,in all these areas many benches are developed1 and steep slopes are only locally developed4 ,northwest ,african ,sector4--,the continental margin from northwest ,morocco to ,dakar is remarkably uniform and rather closely resembles the northeastern ,united ,states sector4 ,the continental shelf and slope are well developed 7,fig4 #ai74 ,the shelf is #ae to #gj miles in width and thus is somewhat narrower than either the ,north ,american shelf or the ,anglo-,french shelf4 ,the shelf break ranges from #ej to #hj fathoms4 ,the continental-slope gradients range from #a3ae to #a3dj and are thus somewhat less steep than in the ,american sectors4 ,prominent benches are common at #cjj1 #fjj1 #hej1 #abjj1 and #afjj fathoms4 ,the continental rise is well developed and is compound4 ,the main contrast between the ,north ,african and ,american sectors is the greater width of the ,african continental rise4 ,off northeastern ,united ,states a line of isolated volcanic peaks cuts across the continental rise and abyssal plain4 ,in the ,north ,african continental margin volcanic peaks are larger1 more numerous1 and lie in coalescing lines or along ridges4 ,the ,cape ,verde and ,canary groups lie in the continental rise near the outer edge of the upper continental rise4 ,all provinces except the continental shelf widen from ,gibraltar southward toward ,cape ,verde4 ,on profile ,e-#aa off ,casablanca the distance from the shelf break to the lower continental rise is only #ej miles as compared with a similar measurement of #ejj miles at ,cape ,verde4 ,off ,casablanca the continental slope extends to #adjj fathoms where the gradient drops to less than #a3dj from #a3aj-a3bj on the continental slope4 ,the upper continental rise which widens to more than #ajj miles farther south is only poorly developed off ,morocco4 ,no other deep-sea echo-sounding profiles are available for the ,moroccan continental margin4 ,surveys of the continental slope made by the ,french ,hydrographic ,service during the past few years will1 when published in full1 undoubtedly provide much valuable information on the topographic benches in this important area 7,grousson1 #aieg74 ,illustration3 ,,heezen et al41 ,,pl4 #h ,,figure #a4 ,,continental ,,rise ,,west ,,of ,,st4 ,,nazaire1 ,,france ,,figure #b4 ,,biscay ,,abyssal ,,plain4 ,,note ,,small ,,mid-,,ocean ,,canyon ,,figure #c4 ,,biscay ,,abyssal ,,plain ,,pdr ,,records ,,european ,,continental ,,rise ,,and ,,biscay ,,abyssal ,,plain ,depth in fathoms4 ,illustration3 ,heezen et al41 ,,pl4 #i ,,figure #a4 ,,small-,,scale ,,roughness1 ,,upper ,,continental ,,rise ,,figure #b4 ,,rolling ,,topography1 ,,upper ,,continental ,,rise ,,figure #c4 ,,cape ,,verde ,,abyssal ,,plain ,,figure #d4 ,,abyssal ,,hills ,illustration3 ,heezen et al41 ,,pl4 #aj ,,pdr ,,record ,,of ,,abyssal ,,hills1 ,,southeast ,,of ,,bermuda ,,rise ,note sub-bottom echos from beneath intermontane basin floor4 ,depth in fathoms4 ,illustration3 ,heezen et al41 ,,pl4 #aa ,area of each photograph is about #f by #h feet4 ,,plate #aa4--,,ocean-,,bottom ,,photographs ,,on ,,the ,,continental ,,margin ,,and ,,ocean-,,basin ,,floor ,,figure #a4 7,station ,t#a-c1 photo #bg7 ,depth #bfj fathoms1 location #dg #db,n41 #jg #cd,w41 just below shelf break west of ,st4 ,nazaire1 ,france4 ,note small ripples which appear to be superimposed on larger ripples4 ,,figure #b4 7,station ,t#a-c1 photo #g7 ,depth #bhe fathoms1 location several hundred feet from photograph in ,figure #a4 ,note holothurians and solitary coral attached to rocks4 ,ripple marks are less prominent than in ,figure #a4 ,,figure #c4 7,stations ,t#a-af1 photo #bh7 ,depth #bfjj fathoms1 location #df #ej,n41 #aa #be,w41 northern part of ,biscay ,abyssal ,plain4 ,note tracks of bottom crawlers1 and the prominent conical mounds1 each with a central hole4 ,,figure #d4 7,station ,t#a-ah1 photo #bi7 ,depth #bfej fathoms1 location #dc #ef,n41 #aa #ab,w41 southern part of ,biscay ,abyssal ,plain4 ,note meandering ridge made by subsurface burrower4 ,note also starfish1 upper left1 and quantity of fecal pellets and holes in the bottom4 ,,figure #e4 7,station ,t#a-bj1 photo #ec7 ,depth #bhej fathoms1 location #db #ah,n41 #ad #dg,w41 northeastern part of ,iberia ,abyssal ,plain4 ,note holes with converging tracks and large mound in upper right4 ,,figure #f4 7,station ,t#a-eh1 photo #ad7 ,depth #cjgb fathoms1 location #bi #ag,n41 #eg #bc,w41 ,abyssal ,hills southeast of ,bermuda ,rise4 ,the round objects are manganese nodules4 ,note shark's tooth in lower right4 ,note also small holes indicating bottom dwellers1 and meandering raised ridge of sub-bottom burrower4 ,of particular interest are the small moats surrounding many of the nodules2 they are probably scour marks caused by bottom currents4 ,these currents must be very gentle since none of the nodules seems to show evidence of recent rolling4 ,positions of stations shown on ,plate #cj4 ,profile ,e-#ab passes from the ,african coast between ,fuerteventura and ,gran ,canary toward the northeast4 ,here the continental slope extends only to #ajjj fathoms4 ,the ,canary ,islands rise abruptly from the continental rise4 ,except for gradients of the order of #a3ae on the steep slopes of these volcanic islands the gradients of the continental rise are #a3cjj-a3ajjj4 ,profiles ,e-#ac and ,e-#ad end on the east near ,gran ,canary and thus do not show most of the upper continental rise4 ,they do show the remarkably wide and nearly level lower continental rise which reaches a width of more than #ejj miles4 ,profiles ,e-#ae and ,e-#af lie off ,spanish ,sahara4 ,in both profiles the gradient is #a3aj to #a3bj between the #ej-;fathom shelf break and a bench at #cjj-ejj fathoms4 ,in both profiles the gradient drops below #a3dj at about #abjj fathoms4 ,both profiles show numerous prominent benches on the continental slope4 ,the upper continental rise with gradients of #a3cej-a3abjj extends to the western limit of the profiles4 ,in profiles ,e-#ag and ,e-#ah the continental slope becomes gentler1 and only in the upper #ejj fathoms of ,e-#ah does the gradient exceed #a3be4 ,the upper continental rise is about #fj miles wide with depths predominantly about #afjj fathoms1 and the lower continental rise lies at about #bajj fathoms and is very smooth4 ,illustration3 ,,figure #ai4--;,continental-margin provinces3 ,type profiles off ,northwest ,africa ,profiles ,e-#ai1 ,e-#bj1 and ,e-#ba cross the continental margin off ,dakar and the ,cape ,verde ,plateau which rises from the lower continental rise4 ,the ,cape ,verde ,plateau consists largely of the coalescing bases of the volcanic ,cape ,verde ,islands4 ,the lower continental rise and the abyssal plain reach their maximum width at this latitude4 ,the width of the ocean1 the width of the ,mid-,atlantic ,ridge1 the width of the abyssal hills1 and the depth at the axis of maximum depth all reach their maximum values for the ,north ,atlantic at this point4 ,the characteristics of the continental rise in this sector are listed in ,table #b4 ,the reliability of these figures is much poorer than those given for northeastern ,united ,states1 owing to the smaller number of profiles in this sector4 ,,table #b4--;,general characteristics of the continental rise northwest ,africa ,sector ,values measured from ,profiles ,e-#aa to ,e-#ba ,depth ,segment ,upper edge ,lower edge ,gradient ,width ,upper continental rise #a #abjj #bjj #aejj #bjj #a3ij #cj #cj #aj8 #b #aejj #bjj #afjj #bjj #a3bjj #ajj #cj #ae8 #c #afjj #bjj #ahjj #ajj #a3ajj #ej #be #ae8 ,lower continental rise #a #ahjj #ajj #bjjj #ajj #a3djj #bjj #ge #ej #b #bjjj #ajj #bjjj #ajj #a3aejj #ejj #aej #ej #c #bjjj #ajj #bgjj #ajj #a3ejj #bjj #bjj #ej ,abyssal plain #bgjj #ajj #cjjj #ge #a3abej #bej #bjj #ej ---------------------------------------- ---------------------------- ,a famous submarine canyon1 the ,fosse de ,cayar1 lies just north of ,cape ,verde4 ,other submarine canyons are certainly present in the sector since any profile parallel to the strike of the topography reveals large irregularities probably related to canyons4 ,echograms 7,pls4 #i1 #ac7 taken in the continental rise in this sector show distinct contrasts in the topographic detail of the sea floor4 ,the rugged topography of the abyssal hills 7,pl4 #i1 fig4 #d7 contrasts sharply with the nearly flat1 extremely smooth abyssal plain4 7,pl4 #i1 fig4 #c74 ,the continental rise is nowhere so smooth nor so flat as the abyssal plain4 ,the continental rise ranges from #aj- to #bj-;fathom rolling hills #e-aj miles in width to #b- to #e-;fathom hills a few hundred feet across 7,fig4 #ai74 ,at the seaward edge of the abyssal plain the echo sounder penetrates the bottom to reveal interfaces #e-bj fathoms below 7,pl4 #ac1 ,fig4 #d74 ,sub-bottom penetration of #e-ae fathoms is occasionally encountered on the continental rise on local topographic highs4 ,lower continental-rise hills of the type observed off eastern ,united ,states have not been observed off ,africa4 ,,benches ,,and ,,terraces ,,of ,,the ,,continental ,,margin ,the topography of the continental margin provinces is divided into a series of benches or terraces4 ,the largest are the continental shelf and slope 7continental terrace7 and the upper and lower continental rise4 ,superimposed on each of these major features is a series of smaller benches and terraces which range from features a few miles wide to simple breaks in the gradient of the continental slope4 ,many of these features can be traced for hundreds of miles 7,heezen et al41 in press72 some are intermittent1 others change in depth with distance along the shelf2 still others are only locally developed4 ,we can propose at least four possible origins for terraces or benches3 7#a7 ancient shore features2 7#b7 structural 7or rock7 benching2 7#c7 block faulting2 and 7#d7 landslide or slump scars4 ,the submerged terraces within a few hundred feet below present sea level can probably best be explained as ancient beaches formed during the lower sea levels of the ,pleistocene4 ,the fact that the same levels are found along coasts of diverse geology and tectonic development supports the eustatic origin of terraces between sea level and #gj-ajj fathoms4 ,the gradients of the continental shelf are so low and the benches are so persistent that block faulting and slump scars are excluded as general explanations4 ,the benches of the continental slope extend to depths of #aejj fathoms and vary in depth from point to point along the continental slope4 ,these cannot be ,pleistocene eustatic levels unless we consider that they were formed prior to recent large crustal deformations4 ,again the persistence of the benches for many miles argues against a fault-scarp or slump-scar hypothesis4 ,thus1 while the benches of the continental shelf are probably ancient beaches1 particularly those traced at the same depth for thousands of miles1 the benches of the continental slope are probably rock benches1 while some may represent step faulting4 ,,submerged ,,beaches ,,on ,,the ,,continental ,,shelf3 ,in ,table #c the depths of terraces or persistent levels of the continental shelf are listed for selected points in the ,north ,atlantic4 ,there is a remarkable uniformity in these data2 the same levels are found near ,newfoundland1 in ,florida1 and on oceanic islands far from the glaciated areas4 ,on the basis of data obtained in the ,north ,atlantic it is not possible to date the different terraces1 but probably most were formed in the period between #ab1jjj and #e1jjj years ,b4,p4 when the sea rose in consequence of the melting of the ,wisconsin glaciers4 ,coring and dredging on these submerged ancient beaches could probably produce material datable by the radiocarbon method4 ,,table #c4--;,depth 7in fathoms7 of prominent continental-shelf terraces ,each column based on only one nonprecision echogram ,st4 ,charles- ,bar ,st4 ,placentia,john's1,norfolk1ton1 ,bimini1,miami1bados1,vincent1,dakar,dak ar ,bay1 ,nfd4,nfd4 ,va4 ,s4 ,c4 ,b4,w4,i4 ,fla4 ,b4,w4,i4,c4,v4,i4 ,north,south #aj #ab #aj #h #aj #h #aj #ae #ae #ae #bj #ah #bj #bj #ah #bj #bj #be #bd #cj #cj #bh #cj #bh #bh #ce #ch #ce #ce #cb #dj #ch #ch #ch #db #de #db #de #db #de #ej #ej #ee #ee #eh #ef #ed #ee #ee #fh #fe #fh #fe #fj #gb #gf #gb #hj #hj #hj #hj #he #ha #hj #gh ---------------------------------------- ------------------------------------- ,,continental ,,margin ,,benches3 ,on each profile across the continental margin is a series of benches and changes in gradient which range from the shelf break to slight changes in gradient on the continental slope4 ,if a field geologist enters a new area of sedimentary rocks where road cuts do not exist he invariably goes to the stream valleys1 and here he gets his first and best view of the geologic section4 ,the stream's gradient is adjusted to the resistance of the rocks over which it cuts1 and the form of the valley-side slopes reveals the nature of the underlying rocks even if they are grassed over4 ,this obvious field method had never been fully applied to the continental margin4 ,stetson 7#aicf7 dredged in the canyons of ,georges ,bank1 and his hauls included ,cretaceous sandstones and ,tertiary marls and green sands4 ,he concluded that the canyons had been cut deep into the continental margin to expose the underlying ,cretaceous rocks1 but he considered the continental slope the product of depositional processes4 ,however ,upham 7#ahid7 had suggested that the continental slope formed a continuous outcrop of ,tertiary and ,cretaceous sediments from ,newfoundland to ,florida1 a suggestion the writers consider quite probable4 ,that is to say1 an analogy can be made between the continental slope and one face of the ,grand ,canyon or to an erosional escarpment bounding a high mesa or plateau like the ,book ,cliffs of ,utah and ,colorado4 ,only a few areas of the world are sufficiently well sounded to provide data for a study of structural benches4 ,one cannot expect to see identical structural benches in each profile even across a slope composed of a laterally uniform series of horizontal beds of contrasting lithologies4 ,the exact mode of erosion1 the local system of jointing1 and chance variations in a number of other variables make it necessary to have a large number of closely spaced1 accurately located profiles4 ,we are fortunate that the ,coast and ,geodetic ,survey has surveyed virtually the entire continental slope from ,georges ,bank to ,norfolk1 ,virginia4 ,almost all these sounding lines are run at right angles to the strike of the topography and are thus suitable for analysis of structural benches4 ,in this same area the dredgings of ,stetson 7#aicf7 on ,georges ,bank and the ,esso ,hatteras ,light test provide us with information on the stratigraphy of the sediments which form the continental shelf and slope4 ,the seismic work of ,ewing and collaborators 7#aicg et seq47 provides us with further information on the dips and on the depths of a number of sedimentary rock series of contrasting lithology4 ,fishermen began finding fossiliferous rocks on ,georges ,bank well over a century ago4 ,they were not particularly pleased to obtain rocks instead of fish and generally threw the accursed rocks back into the sea4 ,some curious fishermen brought a few of the rocks to shore1 however1 and in time some of these were received by the museums 7,upham1 #ahid2 ,dahl1 #aibe74 ,these rocks contain ,tertiary and ,cretaceous fossils4 ,the depths and positions of recovery of the rocks were generally unknown to the museums1 and no clear idea could be gained of the exact occurrence of this material4 ,stetson 7#aicf2 #aidi7 conducted a series of scientific dredging operations in the ,georges ,bank area4 ,his aim was to recover more of these older rocks from known depth ranges and positions4 ,he concluded that the older rocks outcrop only in the submarine canyons4 ,he found no consistent depth ranges for the series of ,miocene and ,upper ,cretaceous rocks obtained4 ,illustration3 ,,figure #bj4--;,georges ,bank canyons ,chart shows position of sounding lines and dredge hauls used to construct projected profile and inferred geologic section shown in ,figure #ba 7a74 ,sounding lines from ,coast and ,geodetic ,survey ,chart #acac4 ,in the ,georges ,bank area a series of prominent benches continues along the continental slope4 ,if these are structural benches we should be able to trace them up the canyons and thus determine the dip of the formations4 ,if the benches are the result of step faulting or landslide scars they would not extend up the canyons4 ,in order to test these alternatives1 a series of profiles has been plotted from the surveys of the ,coast and ,geodetic ,survey4 ,a line was drawn which paralleled most of the contours of the continental slope for #bj miles or more 7,fig4 #bj74 ,a second line was drawn at right angles to this first strike line4 ,all sounding lines in the area were projected to this second dip line along lines parallel to the strike line1 and plotted as a composite projected profile 7,fig4 #ba74 ,if the first line was essentially the strike of rock layers then we should be able to determine the dip of the beds by picking the successive benches as they occur on successive profiles across the canyon4 ,in ,figure #ba the results of the analysis of ,oceanographer and ,hydrographer canyons are presented4 ,the dredge hauls by ,stetson 7#aidi7 have also been projected on this profile4 ,we see that a major bench occurs at ,a which passes below the hauls in which fossiliferous ,navarro 7,upper ,cretaceous7 was obtained and through the upper limit of the hauls where ,matawan 7,upper ,cretaceous7 was obtained4 ,thus if this horizon or one closely parallel to it is the ,navarro-,matawan contract1 the apparent discrepancies of the depth ranges of ,stetson's dredge hauls are explained4 ,much more important to the present study is the dating of a prominent structural bench4 ,illustration3 ,,figure #ba4--,two projected profiles of ,georges ,bank canyons ,location of soundings for profile 7a7 shown in ,figure #bj4 ,soundings projected along strike to construct profile4 ,soundings for both profiles taken from ,coast and ,geodetic ,survey ,chart #acac4 ,illustration3 ,,figure #bb4--;,geologic section at ,cape ,hatteras1 ,virginia ,well logs from ,swain 7#aidg7 and ,spangler 7#aiej74 ,four sounding profiles made by ,r4 ,v4 ,,atlantis are projected to profile4 ,note that resistant formations form prominent structural benches on continental slope4 ,the ,esso ,hatteras ,light ,no4 #a test encountered crystalline rock at #afdj fathoms depth1 beneath ,lower ,cretaceous strata 7,spangler1 #aiej74 ,the several holes drilled in the vicinity revealed remarkably constant dips over a wide area4 ,this is in fact true of the whole coastal plain4 ,since the ,hatteras well is only #ag miles from the continental slope1 it seems reasonable to project the dips to the continental slope4 ,we can then observe whether prominent benches on the continental slope correlate with resistant strata in the well4 ,we find 7,fig4 #bb7 that they do4 ,in the area between ,cape ,hatteras and ,nova ,scotia several cores have revealed reworked ,eocene1 ,miocene1 and ,cretaceous ,foraminifera4 ,in #aidg ,northrop and ,heezen 7#aiea7 obtained a photograph and a core at #ejj fathoms on the continental slope4 ,the core contained ,eocene 7,jackson7 sediments1 and the photograph showed a rock ledge below the marl sampled4 ,although sediment cores1 particularly those of reworked material1 do not provide as reliable information as dredge hauls1 this outcrop of un-reworked ,eocene may also be used in dating the structural benches of the continental slope4 ,the structural benches between ,cape ,hatteras and ,cape ,may are remarkably uniform and persistent 7,fig4 #bc74 ,on the basis of the extrapolation shown in ,figure #bb1 the structural benches in this area have been correlated with the formations encountered in the ,hatteras well4 ,north of ,cape ,may a major angular unconformity separates the late ,tertiary and ,cretaceous formations4 ,eocene has not been found north of ,nantucket4 ,upper ,cretaceous has been found at about #djj fathoms off ,georges ,bank 7,fig4 #ba71 and ,lower ,cretaceous has been dredged at #bjj fathoms off ,banquereau ,bank1 ,nova ,scotia4 ,between #aide and #aiej workers on the ,,atlantis made several sounding profiles east of ,georgia1 ,north ,carolina1 and ,south ,carolina4 ,each crossed the precipitous ,blake ,escarpment4 ,it was quite clear that no sediment could be accumulating on such a steep escarpment and that beds of ancient sediments and perhaps crystalline rocks must outcrop on the escarpment4 ,in #aidi and #aiej a few cores were taken on the escarpment which encountered ,miocene and ,eocene sediments in depths of #ejj-hjj fathoms 7,ericson1 ,ewing1 and ,heezen1 #aieb74 ,the marked similarity of all topographic profiles further supported the view that the escarpment was formed by the outcrop of an orderly sequence of horizontal sedimentary rock layers4 ,with this specific problem in mind a cruise was made to the ,blake-,bahama area on the research vessel ,,atlantis1 in #aiea4 ,more than #ej cores were obtained4 ,sediments of ,recent to ,upper ,cretaceous age were obtained on the ,blake ,escarpment and from the steep walls of the ,bahama ,channels 7,ericson1 ,ewing1 and ,heezen1 #aieb74 ,seismic-refraction work by ,katz and ,ewing 7#aiee7 and ,nafe et al4 7unpublished7 and reflection work by ,ewing and ,landisman 7unpublished7 have revealed that distinct seismic interfaces can be traced into the structural benches on the ,blake ,escarpment4 ,the ancient sediments from the ,blake ,escarpment and the log of the ,andros well allow the dating of some of these formation contacts4 ,at present the most prominent bench at #abjj-aejj fathoms appears to mark the base of the ,upper ,cretaceous4 ,dredging and further coring on the ,blake ,escarpment below #adjj fathoms is one of the most promising projects of its type despite the great difficulties involved4 ,illustration3 ,,figure #bc4--;,correlation of structural benches off northeast ,united ,states ,soundings by ,coast and ,geodetic ,survey2 #ce #cj,n4-#ch #cj,n4 ,lee 7#aiea71 who made a topographic study of ,exuma ,sound1 ,bahamas1 traced several prominent benches through #ea cross sections of the sound4 ,illustration3 ,,figure #bd4--;,geologic section3 ,western ,europe based on refraction measurements ,data from ,day et al4 7#aief7 and ,hill 7#aieg74 ,geologic ages are those assigned by ,day on the basis of velocity2 they are not based on dredging or drilling4 ,seismic-refraction profiles have been made across the continental slope southwest from the ,english ,channel4 ,these studies were initiated by ,bullard and ,gaskell 7#aida7 and have been most recently reported on by ,day et al4 7#aief74 ,the seismic section of ,day et al4 7#aief7 7,fig4 #bd7 suggests that the prominent bench at #afjj fathoms and the short but steep scarp just below represent the outcrop of the metamorphic basement on the continental slope4 ,it is postulated that the prominent bench at #ijj fathoms may represent the base of the ,mesozoic1 and the smaller bench at #cjj fathoms the base of the ,miocene4 ,tertiary sediments have been obtained from the walls of canyons in the ,bay of ,biscay in depths down to about #aejj fathoms 7,bourcart and ,marie1 #aiea74 ,the age assignments in ,figure #bd are taken directly from ,day et al4 7#aief7 and have not been confirmed by dredging on the continental slope4 ,the writers conclude that the majority of the topographic benches of the continental slope and other category ,,ii provinces are structural benches which reflect the outcrop of resistant rock layers4 ,this of course implies that the continental slope is not a simple depositional feature but a structural or erosional one4 ,since the structural benches are present both in the canyons and on the un-dissected slope1 the occurrence of ,tertiary and ,cretaceous rocks on the continental slope cannot be explained by erosion of submarine canyons into an otherwise depositional terrace in the manner implied by ,stetson 7#aidi74 ,the existence of such persistent benches implies that the entire width of the category ,,ii provinces must be at most only thinly covered by recent sediments4 ,since the discovery of the great importance of turbidity currents and the relatively low slopes necessary for their occurrence1 it has been a great puzzle to the writers how sediments could be permanently deposited on the present continental slope4 ,the answer is simply that they are not4 ,in addition to the turbidity currents which provide a mechanism for the seaward transport of sediment down the continental margin1 deep-ocean currents probably sort and transport much sediment along a course parallel to the continental slope4 ,it has recently been demonstrated 7,swallow and ,worthington1 #aieg7 that velocities of #aj-bj cm_/sec are attained by ocean currents which flow parallel to the continental slope4 ,the particular measurement referred to was made at #afjj fathoms on the continental slope south of ,cape ,hatteras where a #ag cm_/sec southward-moving current was observed4 ,the strong current is not a local phenomenon since it was found in the ,south ,atlantic by ,wst 7#aice7 and is predicted by theories of ocean circulation 7,stommel1 #aieg74 ,photographs of ripple marks on the continental slope 7,see for instance ,fig4 #ac in ,elmendorf and ,heezen1 #aieg7 had indicated high velocities1 but it was not possible to distinguish between a current and an oscillatory origin4 ,the total effect of slides1 slumps1 turbidity currents1 and strong ocean-bottom currents is the removal of most of the unconsolidated ,recent sediments from the continental slope4 ,the deposition of a series of ,mesozoic and ,tertiary sediments on the subsiding margin of the continental block has produced a wedge of sedimentary rock largely of shallow marine facies4 ,each successive strata laid down on the shelf was abruptly terminated at the shelf break by the processes of erosion which continuously or periodically clear the unconsolidated sediment from the continental slope4 ,deposition on the shelf was interrupted by several marine regressions which produced unconformities in the stratigraphic sequence4 ,nafe and ,drake 7#aieg7 observed that the increase of seismic velocity with depth and therefore the increase in compaction with depth is more rapid on the continental shelf than in the deep sea4 ,this is probably in part the result of erosion of previously deposited sediments and sedimentary rocks along the unconformities and in part the result of ground-water cementation during periods of emergence4 ,each unconformity should mark a lithologic change and consequently a change in the resistance to erosion of the rock series4 ,many structural benches may indicate surfaces of unconformity4 ,the most recent unconformity in the sequence lies between the surface of the emerged ,wisconsin continental shelf and the overlying post-glacial shelf sediments4 ,the shelf break is defined as the most prominent break in slope between the continental shelf and continental slope4 ,the most prominent break may locally be a ,pliocene or ,miocene structural bench1 but elsewhere late ,pleistocene or ,recent strata may form the shelf break4 ,rates of subsidence1 erosion1 and sediment supply vary from place to place along the continental shelf1 and the lack of conformity either in depth or in age of the shelf break is thus easily explained4 ,the deeper structure of the continental margin indicates a fundamental structural discontinuity at the base of the continental slope 7category ,,ii provinces74 ,it would seem a small extrapolation to attribute a fault origin to the continental slope4 ,although faulting may have played a large part in the earliest history of the category ,,ii provinces1 alternate periods of sedimentation and marine planation on the continental shelf and long-continued erosion by slumps1 turbidity currents1 and deep-sea currents on the continental slope1 together with a general subsidence of the area1 could have alone produced the characteristic form of the continental terrace4 ,further work on structural benches co-ordinated with a study of ancient sediments from dredges and cores should enable us to draw a geologic map of the continental slope of eastern ,united ,states and ,europe 7,heezen et al41 in preparation74 ,,geology ,,and ,,geophysics ,,of ,,continental ,,margin ,,physiographic ,,provinces ,seismicity of the continental-margin provinces4--,plate #bi shows the distribution of epicenters in the ,north ,atlantic4 ,except in the ,puerto ,rico ,trench and the adjacent ,antilles ,arc1 earthquakes are exceedingly rare in the continental-margin provinces of the ,north ,atlantic4 ,from the ,bahamas through the ,grand ,banks the only earthquakes reported since #aiaj are two near the ,laurentian ,channel4 ,in the eastern ,atlantic an earthquake belt crosses the continental margin near ,gibraltar but does not seem to be directly associated with the ,atlantic continental margins4 ,if the continental slope in the area covered by ,plate #bi is a fault scarp1 we must infer that the motion has now been arrested4 99 99 99 99 99 ,magnetic anomalies and continental-margin provinces4--,the first continuously recorded total-intensity magnetic data for the ,atlantic were obtained in #aidf on a flight from ,long ,island1 ,new ,york1 to ,bermuda1 and return 7,keller et al41 #aied74 ,the first data from a ship-towed magnetometer were obtained in #aidh 7,heezen1 ,ewing1 and ,miller1 #aiec74 ,the initial measurements showed 7#a7 several large 7 #cjj7 anomalies on the continental shelf1 7#b7 a large 7 #ejj7 anomaly over the continental slope1 7#c7 an exceptionally smooth field over the category ,,iii provinces1 7#d7 rough fields with #e- to #ae-mile wide #ajj to #bjj anomalies over oceanic ridges and rises1 7#e7 enormous anomalies 7 #ajjj7 over seamounts and islands1 and 7#f7 large anomalies 7 #ejj7 over the crest of the ,mid-,atlantic ,ridge4 ,the large anomalies on the continental shelf were considered to indicate large volcanic cones buried by the sediments of the continental shelf 7,miller and ,ewing1 #aief74 ,the anomaly over the continental slope was considered to be the magnetic-edge effect associated with the abrupt edge of the continental block4 ,the rough fields over the oceanic rises and ridges were attributed to variations in the susceptibility of the crustal rocks1 probably related to volcanic extrusions and intrusions4 ,the anomaly over the crest of the ,mid-,atlantic ,ridge was not recognized as a general pattern until later when many measurements were made4 ,the major puzzle for which no explanation was readily obtained was the origin of the smooth field over the continental rise4 ,the smooth or quiet field has been observed on each crossing of the category ,,iii provinces1 and even such a sharp-sided feature as the ,puerto ,rico ,trench failed to show a magnetic anomaly 7,davidson and ,miller1 #aief74 ,we can thus state that all category ,,iii provinces are characterized by a smooth magnetic field4 ,the significance of this point is not yet clear1 but it must be of major importance to the full understanding of the continental margin4 ,crustal structure and continental-margin provinces4--,maurice ,ewing and his associates have made more than #ajjj seismic-refraction measurements to determine the crustal structure of continental margins4 ,most of the published results pertain to the eastern continental margin of the ,united ,states 7,drake et al41 in press71 but much material will soon be published on the continental margin of ,sahara1 ,sierra ,leone1 ,brazil1 ,argentina1 ,guiana1 ,spain1 ,morocco1 the ,gulf of ,mexico1 and the ,caribbean ,sea4 ,in addition extensive work has been accomplished by ,bullard1 ,gaskell1 and ,hill in the western approaches to the ,english ,channel4 ,in some areas seismic1 gravity1 and magnetic measurements were made along the same lines and have been subjected to an integrated analysis 7,worzel and ,shurbet1 #aiee;c74 ,in ,plate #bf four profiles replotted from published sections are shown4 ,each profile is plotted at #dj3a exaggeration1 and depths are indicated in fathoms and kilometers to facilitate comparison with the profiles and topographic descriptions given elsewhere in this paper4 ,some stations which lie up to #ajj miles from a profile have been projected along the strike of the topography4 ,in general each profile indicates 7#a7 a thick lens of sediment and sedimentary rock beneath the continental rise2 7#b7 a major discontinuity in crustal structure at the base of the continental slope2 and 7#c7 a wedge of low-velocity sedimentary rocks 7unconsolidated7 overlying a lens of higher-velocity 7semi-consolidated and consolidated7 sedimentary rocks beneath the continental shelf4 ,the basin1 filled with higher-velocity sedimentary rocks1 is formed by an upturned lip of crystalline basement rocks near the continental slope4 ,local variations in thickness and velocity give rise to interesting minor configurations1 but the basic structure is nearly identical in all the sections4 ,the main contrast is that the category ,,iii provinces are underlain by thick sedimentary rocks in the case of the continental rise1 and successively thinner accumulations of sedimentary rock are associated with the marginal basins and marginal trenches4 ,since the main difference in the continental-margin sections seems to be a greatly enhanced continental-rise sedimentary section to the north as compared with the ,blake ,plateau--,bahama--,puerto ,rico region1 it seems reasonable to conclude that the main difference in the topography is the result of different sedimentation rates or a different time of origin1 rather than of a vastly different structural origin4 ,the sedimentary rock column beneath the continental rise is truly geosynclinal in thickness4 ,whether this great lens of sediment and sedimentary rock will eventually be deformed into a mountain range to form a new addition to the continent as advocated by the accretion school or whether it will lie forever on the sea floor is one of the great speculations of geology4 99 99 99 99 99 ,sediment distribution and physiographic provinces of the continental margin4 ,the recent sediments of the category ,i provinces are largely sands1 silts1 silty lutites1 and carbonates 7,stetson1 #aich2 ,shepard and ,cohee1 #aicf2 ,newell1 #aiee74 ,all these sediments can be assigned to the orthoquartzite suite of ,pettijohn 7#aieg74 ,judging from the ancient sediments dredged from the continental slope and obtained by drilling1 the category ,i provinces have been receiving orthoquartzite sediments at least since the ,cretaceous4 ,in category ,,ii provinces ,recent sediments are either lacking or are very thin4 ,those ,recent sediments which temporarily remain in the province range from foraminiferal lutites1 found in such areas as the ,bahamas1 to silty lutites relatively poor in pelagic fossils1 found in the higher latitudes4 ,in general category ,,ii provinces are characterized by nondeposition or erosion4 ,the sediments of the category ,,iii provinces include both pelagic and clastic terrigenous sediments4 ,the outer ridge is covered by ,globigerina ooze in depths shallower than about #bbjj fathoms and by red clay in deeper areas4 ,the continental rise is generally covered by silty foraminiferal lutites1 but1 where submarine canyon deltas spread out from the mouths of submarine canyons 7,ericson et al41 #aiea1 #aieb71 beds of graded sand and silts from a few centimeters to a few meters in thickness are interbedded with lutites4 ,in the marginal trenches and marginal basins graded calcareous sands alternate with low-carbonate lutites4 ,the category ,,iii provinces of northwest ,africa are dominated by two groups of volcanic islands and seamounts which contribute flows and volcanic detritus to the continental-rise sediments4 ,in general the category ,,iii provinces are dominated by sediments ascribable to the graywacke suite of ,pettijohn 7#aieg74 99 99 99 99 99 ,past1 present1 and future of continental-margin physiographic provinces4--,it takes only a little imagination to see a historical or genetic sequence in the four profiles of ,plate #bf4 ,the ,puerto ,rico ,trench--outer-ridge profiles thus may represent a continental margin in youth1 the ,blake--,bahama--outer-ridge profile a margin in late youth or early maturity1 and ,newfoundland and northeast ,united ,states profiles a margin in late maturity or old age4 ,the lens of sediments that has filled the marginal trench off northeastern ,united ,states is truly geosynclinal in thickness 7,drake et al41 in press74 ,the sediments of the shelf lens are similar in lithology to the orthoquartzite suite of a mio-geosyncline 7cf4 ,kay1 #aiea71 and the thicker continental-rise lens is probably similar in lithology to the graywacke-volcanic suite of a eugeosyncline4 7,kay1 #aiea74 ,it seems virtually certain that ancient orthogeosynclines were1 before deformation1 closely analogous to the continental margins4 ,the major problem is completing the sequence from filled geosyncline to folded mountains is the mechanism by which the earth's crust beneath the geosyncline thickens by #bj-cj km4 ,although we cannot predict the future of the present continental margin with any assurance until the mechanism of thickening is understood1 it seems probable that before deformation the older orthogeosynclines were similar in most details to the modern continental margins4 ,it seems possible that the present continental margins will in some future geological period be uplifted into folded mountains4 ,,ocean-,,basin ,,floor ,,general ,,description ,the second of the three basic topographic divisions of the oceanic depression is the ocean-basin floor4 ,included in this division are those provinces of the oceanic depression that are not included in the continental margin or the mid-oceanic ridge4 ,the ocean-basin floor is divided into three categories3 7#a7 abyssal floor1 7#b7 oceanic rises1 and 7#c7 seamounts and seamount groups4 ,the first category includes two types of provinces1 abyssal plains and abyssal hills1 which occupy the deepest portion of the ocean-basin floor4 ,included in these provinces are such features as abyssal gaps and mid-ocean canyons4 ,the second category includes the larger positive features of the ocean-basin floor1 and the large seamounts and seamount groups fall in the third category4 ,the landward limit of the ocean-basin floor is the #a3ajjj gradient isopleth along the continental margin4 ,along the mid-oceanic ridge the boundary is taken as that scarp or scarp zone where the average level rises appreciably above the axis of maximum depth of the basin floor4 ,broad elevations which rise above the basin floor as isolated rises are termed oceanic rises and are included in this discussion even though they may be structurally more closely related to the mid-oceanic ridge or the continental margin4 ,,abyssal ,,plains ,general discussion4--,an abyssal plain has been defined 7,heezen1 ,ewing1 and ,ericson1 #aied7 as an area of the deep-ocean floor in which the ocean bottom is flat and the slope of the bottom is less than #a3ajjj4 ,abyssal plains have been found in all oceans1 characteristically at the foot of the continental rise4 ,koczy 7#aied2 #aief7 and ,gaskell and ,ashton 7#aied7 have described the abyssal plain south of the ,bay of ,bengal4 ,koczy 7#aief7 has described plains in the equatorial ,atlantic on either side of the ,mid-,atlantic ,ridge4 ,on ,expedition ,deep ,freeze workers on the ,,uss ,,glacier1 using a ,,pdr1 discovered an abyssal plain in the ,weddell ,sea4 ,workers on the ,r4 ,v4 ,,vema in #aieg confirmed the existence of abyssal plains in the ,argentine and in the ,cape and ,angola basins of the ,south ,atlantic4 ,menard 7#aiee7 has described abyssal plains off the ,california and ,alaska coasts4 ,abyssal plains are really important and are present off all coasts except those having a long1 continuous1 unfilled marginal trench4 ,the abyssal plains shown on the physiographic diagram have been named in order to facilitate referencing4 ,the abyssal plains of the western ,atlantic between ,newfoundland and the ,west ,indies are best known4 ,the abyssal plain south of ,newfoundland 7,heezen et al41 #aied7 has been named the ,sohm ,abyssal ,plain following the usage of ,murray 7#aiab7 who referred to this area as ,sohm ,deep in several publications4 ,the abyssal plain south of the ,bermuda ,rise referred to as the abyssal plain in the ,nares ,basin 7,heezen1 ,ewing1 and ,menzies1 #aiee2 ,luskin et al41 #aied7 is named on the province chart 7,pl4 #bj7 the ,nares ,abyssal ,plain1 also following the usage of ,murray 7#aiab71 who named this area the ,nares ,deep4 ,the abyssal plain southwest of the ,bermuda ,rise was included in the ,nares ,abyssal ,plain until the discovery in #aiee that the two parts were separated by a steep abyssal gap at #bd ,n4 #fh ,w4 necessitated the splitting off of this plain from the ,nares ,abyssal ,plain4 ,the name ,hatteras ,abyssal ,plain used on the map was suggested by the close proximity of the very prominent ,cape ,hatteras4 ,an abyssal plain is probably present in the ,newfoundland basin1 but no ,,pdr soundings have been obtained in that area4 ,the name ,newfoundland ,abyssal ,plain is suggested subject to confirmation by a precision survey4 ,the outer ridge which runs south from ,cape ,hatteras paralleling the coast lines of the ,bahamas encloses the ,blake-,bahama ,basin 7,ericson1 ,ewing1 and ,heezen1 #aieb72 a narrow abyssal plain is found along its western margin4 ,this plain is named the ,blake-,bahama ,abyssal ,plain4 ,between the ,greater ,antilles and the ,bahama ,banks is a depression called the ,old ,bahama ,channel in the north2 farther south it is known as the ,hispaniola-,caicos ,channel4 ,the ,hispaniola-,caicos ,channel in particular contains an abyssal plain which1 although much smaller than the large1 deep-sea abyssal plains1 has all the characteristics of slope flatness and sediment composition4 ,this is called the ,hispaniola-,caicos ,abyssal ,plain4 ,the smallest1 yet perhaps the most striking1 ,atlantic abyssal plains are those at the bottom of the ,puerto ,rico ,trench at depths of about #dceh fathoms 7#dehe corrected74 ,they exhibit the proper degree of flatness1 low gradient 7,ewing and ,heezen1 #aiee71 and the shallow-water clastic sediments typical of abyssal plains4 ,south of ,cuba in the southwest corner of the diagram lies a major deep-sea trench4 ,only the eastern end of this ,cayman ,trench is shown in the diagram4 ,on the floor of this steep-walled trench lies a narrow trench plain or system of semi-connected trench plains which lie at depths of about #cjjj fathoms south of ,guantanamo1 ,cuba1 but deepen to #cfib fathoms south of the ,cayman ,islands4 ,these are known as the ,cayman ,trench ,plains4 ,this area will be described in more detail in a later publication devoted to the topography of the ,caribbean4 ,in the eastern ,atlantic each abyssal plain has been crossed at least three times by ships employing a ,,pdr1 a coverage which1 although sufficient to establish their existence1 is vastly inferior to the coverage of the western ,atlantic abyssal plains4 ,the ,biscay ,abyssal ,plain occupies a large portion of the ,bay of ,biscay4 ,it is connected by an abyssal gap at #dc #cj,n41 #ab #jj,w41 to the ,iberia ,abyssal ,plain which lies west of the northern two-thirds of the ,iberian ,peninsula4 ,a small abyssal plain west of the ,tagus ,river takes its name from this river4 ,the great abyssal plain which skirts ,madeira on the east and south and extends over a vast area to the west is referred to as the ,madeira ,abyssal ,plain4 ,the ,canary ,islands and associated banks form the boundaries of a small oval depression known as the ,canary ,abyssal ,plain4 ,the vast abyssal plain which skirts the ,african continent west of ,cape ,verde is named the ,cape ,verde ,abyssal ,plain4 ,the eastern margin of the map just reaches the abyssal plain in the western ,mediterranean which ,heezen and ,ewing 7#aiee7 have named the ,balearic ,abyssal ,plain4 ,abyssal plains were not discovered until the use of continuously recording echo sounders was extended to abyssal depths following ,world ,war ,,ii 7,tolstoy and ,ewing1 #aidi74 ,while the early nonprecision echo sounders were sometimes adequate to distinguish the limits of particular plains1 real advances in their study required the development of precision sounders and the extensive use thereof 7,heezen1 ,ewing1 and ,ericson1 #aied74 ,since the very existence of abyssal plains has been known for less than #aj years and only recently have any of them been adequately delineated1 the problem of their nomenclature has never before arisen4 ,in the cases of the ,nares and ,sohm abyssal plains we have taken the name ,murray has given to the deeps in which the plains occur4 ,for ,cape ,verde1 ,iberia1 and ,newfoundland abyssal plains we have followed the name ,wst 7#aidj;b7 proposed for the basin within which the plains lie4 ,the ,biscay1 ,tagus1 ,hatteras1 ,blake-,bahama1 ,hispaniola-,caicos1 and ,balearic have been given the name of a prominent near-by land area1 in accordance with recognized practice4 ,the ,horseshoe ,abyssal ,plain takes its name from the horseshoe-shaped line of seamounts which surrounds it except on the eastern side4 99 99 99 99 99 ,regional description4--,the relief of the abyssal plains is so low that ordinary small-scale exaggerated profiles 7,pls4 #bb1 #bg7 reveal nothing of its detailed character4 ,in a few areas exceptionally good ,,pdr records have been obtained which show relief of a few feet 7,pl4 #ab74 ,,sohm ,,abyssal ,,plain3 ,the best-studied abyssal plain is the ,sohm ,abyssal ,plain south of ,newfoundland4 ,in addition to the #aiec ,,vema ,,pdr survey 7,heezen et al41 #aied7 the area was studied extensively in #aiee and crossed by the trans-,atlantic cruises of #aied and #aief4 ,the plain is ,t-shaped and generally about #bjj miles wide2 depths range from #bgjj to #cjjj fathoms 7uncorrected74 ,the depth increases in each arm of the ,t toward the stem where the slope changes to south4 ,the greatest depth is found at the south boundary of the plain near #bi ,n4 ,in the northern part of the plain small topographic irregularities are unknown1 but toward the south peaks #ej to #ejj fathoms high increase in number until they finally replace the plain4 ,north of the ,bermuda ,rise the plain surrounds a line of huge seamounts4 ,however1 even here no small hills are found4 ,in the strip extending between #cj and #cg ,n41 the east and west boundaries of the plain are formed by scarps #bjj to #hjj fathoms high4 ,the boundary on the north side of the ,bermuda ,rise is formed by a distinct shallowing1 but no scarp is seen4 ,there is some justification for separating the northwest arm of the ,sohm ,abyssal ,plain north of the ,bermuda ,rise from the rest of the ,sohm ,abyssal ,plain since a mid-ocean canyon runs from the northwest to the central sections of the plain4 ,a sill might lie northeast of the northeast tip of the ,bermuda ,rise4 ,here the bottom gradient changes slightly1 and an extremely large magnetic anomaly is associated with the region4 ,however1 the plain narrows only slightly at this point1 and1 since we cannot tell how many individual basins were filled to form an abyssal plain1 we will consider that the ,sohm ,plain now includes the whole area1 keeping in mind that the northwest arm may have only recently merged with the rest4 ,south of ,newfoundland the continental rise merges with the abyssal plain with no scarp or line of hills4 ,here the boundary is taken at the point where the gradient is gentler than #a3ajjj4 ,this is not an entirely arbitrary definition since an appreciable change in gradient generally occurs near this point4 ,south of the boundary the gradient gradually decreases to #a3cjjj at #cg ,n41 beyond which it decreases even more gradually and reaches #a3ejjj at the southern edge of the plain4 ,,hatteras ,,abyssal ,,plain3 ,northeast of the ,bermuda ,rise on a line between ,long ,island 7,n4 ,y47 and ,bermuda a small area of abyssal hills lies between the continental rise on the northwest1 the ,bermuda ,rise on the southeast1 the ,sohm ,abyssal ,plain on the northeast1 and the ,hatteras ,abyssal ,plain on the southwest4 ,although this area has been traversed by more tracks than any area of similar size in the ,atlantic1 the relationships here are still somewhat obscure4 ,this area of some #fjjj square miles is one of irregular relief1 but it is not known if it is of the character of an irregular sill or a complex abyssal gap1 although the latter seems more probable4 ,the northwest margin of the ,hatteras ,abyssal ,plain is abruptly formed by the lower continental rise hills4 ,the eastern boundary is generally distinct and in places is formed by a #ej- or #ajj-;fathom scarp1 but generally it is not so impressive as the east and west boundaries of the ,sohm ,abyssal ,plain4 ,south of about #cd ,n41 the western boundary of the ,hatteras ,abyssal ,plain is formed by the outer ridge4 ,in some sectors the eastern flank of the outer ridge is rather gentle1 and the abyssal plain gently laps the ridge without a sharp break4 ,this boundary is generally sharp north of #bg ,n4 but to the south is less definite4 ,the ,hatteras ,plain slopes southeast to about #ca ,n4 where the direction of slope changes to south4 ,a gradient of about #a3cjjj and depths of about #bijj fathoms are reached at #be ,n4 ,within about #fj miles of ,vema ,gap the plain is broken by numerous mid-ocean canyons which converge on the gap 7,pl4 #ad1 fig4 #c74 ,the ,hatteras ,abyssal ,plain has no known seamounts or sea knolls1 in contrast to the ,sohm ,abyssal ,plain and ,nares ,abyssal ,plain4 ,the sediments of the ,hatteras ,abyssal ,plain resemble the northern abyssal plains in having many beds of quartz silts 7,pl4 #bh7 and contrast sharply with the ,blake-,bahama ,abyssal ,plain where calcareous sands are abundant4 ,on the west the outer ridge forms a continuous barrier to turbidity-current sediments coming from the near-by ,bahamas so that the only source of turbidity-current sediments is from the ,cape ,hatteras region to the north or possibly from the ,hudson ,canyon via the suspected abyssal gap mentioned above4 ,the type of sediment is entirely consistent with the gradient of the plain which slopes southward from the ,hatteras region4 ,illustration3 ,heezen et al41 ,,pl4 #ad ,,figure #a4 ,,sub-,,bottom ,,echoes ,,on ,,record ,,from ,,southern ,,bermuda ,,rise ,,figure #b4 ,,mid-,,ocean ,,canyon ,,no4 #b ,,figure #c4 ,,mid-,,ocean ,,canyon ,,in ,,hatteras ,,abyssal ,,plain1 ,,west ,,of ,,vema ,,gap ,,pdr ,,records ,,of ,,mid-,,ocean ,,canyon ,,no4 #b ,,and ,,canyons ,,at ,,vema ,,gap ,depth in fathoms4 ,illustration3 ,heezen et al41 ,,pl4 #ae ,area of each photograph is about #f by #h feet4 ,,plate #ae4--,,ocean-,,bottom ,,photographs ,,of ,,seamounts ,,figure #a4 7,station ,v#d-ab1 photo #af7 ,depth #gjj fathoms1 location #ce #ab,n41 #ae #ah,w41 on seamount of the ,horseshoe ,group4 ,note bioclastic debris lodged in depressions on the rocky bottom4 ,photographs shown in ,figures #a1 #b1 and #c are no more than a few hundred feet apart4 ,,figure #b4 7,station ,v#d-ab1 photo #aj7 ,depth #gjj fathoms1 location #ce #ab,n41 #ae #ah,w4 ,rippled sandy bottom4 ,,figure #c4 7,station ,v#d-ab1 photo #g7 ,depth #gaj fathoms1 location same as ,figures #a and #b4 ,note current ripple marks4 ,the photograph indicates an appreciable current from left to right4 ,,figure #d4 7,station ,v#d-af1 photo #ai7 ,depth #aajj fathoms1 location #ce #jg,n41 #ac #jd,w41 on the side of ,ampere ,seamount4 ,note winnow row of dark and light gravel-sized detritus which resembles similar material on the ,rift ,mountains shown in ,figure #a of ,plate #ai4 ,,figure #e4 7,station ,v#d-ah1 photo #bf7 ,depth #ge fathoms1 location #ce #aj,n41 #ab #ee,w41 near the top of ,ampere ,seamount4 ,,figure #f4 7,station ,v#d-ad1 photo #dg7 ,depth #aajj fathoms1 location #ce #ab,n41 #ae #bb,w4 on same seamount as ,figures #a-c4 ,bottom appears to consist of light-colored sediment thinly veiled by dark coarser sediment4 ,the white polka dots appear to represent piles of the underlying light sediment brought to the surface by burrowers4 ,positions of stations shown on ,,plate #cj ,,blake-,,bahama ,,abyssal ,,plain3 ,the ,blake-,bahama ,basin is a long narrow basin between the great ,blake ,escarpment and calcareous ,bahama ,island banks on the west and the outer ridge on the east4 ,a narrow abyssal plain #bj to #gj miles wide spreads out from the base of the escarpment 7,pl4 #e1 fig4 #c74 ,the plain is shallowest and widest just east of the ,northeast ,providence ,channel and deepens and narrows toward its northern and southern ends4 ,sediment cores taken #fj miles off the mouth of ,northeast ,providence ,channel contained graded beds of calcareous sand a few meters thick 7,ericson et al41 #aieb74 ,the material was obviously derived from the ,bahamas1 presumably through the action of turbidity currents running out through the ,providence ,channels1 the southern entrance of ,exuma ,sound1 and the numerous submarine canyons which dissect the slopes off the islands4 ,the depth of the plain ranges from #bfjj to #bgej fathoms1 and its area is about #gjjj square miles4 ,,nares ,,abyssal ,,plain3 ,south and southeast of the ,bermuda ,rise lies the ,nares ,plain1 a #cg1jjj-square-mile abyssal plain that slopes eastward from ,vema ,gap toward the ,mid-,atlantic ,ridge4 ,from #fb to #fd ,w4 its northern and southern boundaries are abrupt1 and only three or four small abyssal hills have been observed in the plain4 ,east of #fd ,w4 the gradient of the plain exceeds #a3bejj1 and the frequency of hills increases until at #fa ,w4 the plain consists of a series of fingers which extend into the abyssal hills4 ,the sediment cores obtained in the ,nares ,abyssal ,plain consist of alternating red clays and quartz silts 7,ericson et al41 #aieb2 in press74 ,the ,nares ,abyssal ,plain is the deepest of the broad abyssal plains of the ocean-basin floor4 ,it is also the farthest from the land4 ,if the turbidity currents smoothed the ,nares ,plain they would all have had to flow through ,vema ,gap since the outer ridge-trench complex to the south prevents currents from this area from reaching the ,nares ,abyssal ,plain4 ,the idea of a route through ,vema ,gap is supported by the fact that the plain slopes eastward from the gap4 ,,hispaniola-,,caicos ,,abyssal ,,plain3 ,the depression between the ,bahamas and the coasts of ,cuba and ,hispaniola deepens east of ,cay ,lobos and reaches its maximum depth of #bbbj fathoms northwest of ,cape ,francis ,viejo of ,hispaniola4 ,at ,cay ,lobos the channel is a steep ,v-shaped depression with a maximum depth of #djj fathoms1 but to the east this ,v-shaped channel opens out to an abyssal plain about #aejj fathoms deep4 ,between this point and ,great ,inagua ,island the flat floor slopes east reaching a depth of #aege fathoms just southwest of ,inagua4 ,this portion is called the ,old ,bahama ,abyssal ,plain4 ,south of ,great ,inagua is another ,v-shaped channel in which the depth drops from #agjj fathoms on the west to #bbjj fathoms on the east4 ,from this point to ,cape ,francis ,viejo the ,hispaniola-,caicos ,abyssal ,plain is nearly flat4 ,sediments collected from this plain confirmed the turbidity-current origin of the smooth topography4 ,the cores contained plant debris1 shallow-water fossils1 and a variety of reworked older material 7,ericson1 ,ewing1 and ,heezen1 #aieb2 ,ewing and ,heezen1 #aiee2 ,ericson et al41 #aiee74 ,,puerto ,,rico ,,trench 7,,abyssal7 ,,plains3 ,a trench plain is an abyssal plain in the bottom of a deep-sea trench4 ,since the discovery of the ,puerto ,rico ,trench 7,abyssal7 ,plains similar features have been reported for the ,middle ,america ,trench 7,fisher1 #aied71 the ,kurile-,kamchatka ,trench 7,udintsev1 #aiee71 and the ,peru-,chile ,trench 7,zeigler1 #aieh74 ,two trench plains are known from the ,puerto ,rico ,trench4 ,the smaller one occupies a basin south of a median ridge1 and the larger one lies along the deep axis of the trench4 ,they range in width from #a-b miles to about #ab miles4 ,sediment cores taken in the trench plain contained beds of graded calcareous sand containing fragments of ,halimeda and shallow benthic ,foraminifera 7,ericson1 ,ewing1 and ,heezen1 #aieb74 ,the depth of the larger trench plain ranges only slightly from #dceh fathoms 7#dehe fathoms corrected74 ,the trench shallows eastward1 and the plains disappear4 ,,cayman ,,trench 7,,abyssal7 ,,plains3 ,the ,cayman ,trench contains trench plains very similar to those in the ,puerto ,rico ,trench4 ,the limits of the ,cayman ,trench ,plains shown on the physiographic diagram may not be too reliable2 it has not been redrafted since the most recent tracks shown on the track chart were obtained4 ,,biscay ,,abyssal ,,plain3 ,the ,bay of ,biscay is occupied by a large abyssal plain which begins a few miles north of the northern limit of the map and ends at the ,theta ,gap at #dc #cj,n4 ,the plain ranges from #beej to #bfej fathoms in depth and is about #bjj miles wide4 ,cores of graded sand and silt have been obtained from the floor of the plain4 ,several mid-ocean canyons #c to #e fathoms deep and a quarter of a mile to #b miles wide have been observed in the plain 7,pl4 #h71 but data are not sufficient to determine their exact courses4 ,it is suggested that they converge on ,theta ,gap and that some may be extensions of submarine canyons of the continental slope4 ,,iberia ,,abyssal ,,plain3 ,south of ,theta ,gap and west of the northern third of the ,iberian ,peninsula lies an oval abyssal plain of about #be1jjj square miles4 ,the depth of this plain ranges from #bggj fathoms near ,theta ,gap and at the base of the continental rise to #bhbj fathoms near the eastern margin of the abyssal hills province4 ,the plain fans out from ,theta ,gap and gradually merges with the normal westward slope from the continental rise of north ,iberia4 ,,tagus ,,abyssal ,,plain3 ,west of the canyons off the mouth of the ,tagus lies a small circular plain of #gajj square miles4 ,its depth ranges from #bfej to #bgjj fathoms1 and it slopes westward with slightly fan-shaped contours extending from the mouths of the two large canyons4 ,a recent sediment sampling campaign revealed numerous graded silt and sand layers in the plain 7,pl4 #bh74 ,,horseshoe ,,abyssal ,,plain3 ,a small abyssal plain of #ebjj square miles lies in the center of a horseshoe-shaped ring of seamounts1 just west of ,gibraltar4 ,,madeira ,,and ,,cape ,,verde ,,abyssal ,,plains3 ,from ,gibraltar to ,cape ,verde and extending southward to the ,sierra ,leone ,rise at #aj ,n4 a vast abyssal plain parallels the coast of ,africa4 ,for most of its length the western boundary of this plain is #gej miles from the coast4 ,the average width of the plain is #bjj miles1 and it occasionally reaches #cjj miles4 ,an eastward extension of the abyssal hills approaches within #bjj miles of the ,canary ,islands1 forming a natural constriction which divides the plain into a northern part1 the ,madeira ,abyssal ,plain1 and a southern part1 the ,cape ,verde ,abyssal ,plain4 ,the ,madeira ,abyssal ,plain occupies #aej1jjj square miles4 ,the ,azores-,gibraltar ,ridge forms its northern boundary1 and the abyssal hills its western boundary4 ,depths near the seaward limit of the plain reach #bigj fathoms4 ,the northern part of the ,madeira ,plain is broken by a series of low scarps 7,pl4 #ac1 fig4 #c74 ,the gradient of the plain between successive scarps is about #a3aejj4 ,the ,cape ,verde ,abyssal ,plain occupies #bjj1jjj square miles of sea floor 7,pl4 #i1 fig4 #c74 ,the transition from abyssal plain to abyssal hills is gradual4 ,many hills are scattered in the plain near the boundary4 ,small scarps of the kind observed in the ,madeira ,abyssal ,plain have not been found4 ,recent soundings southwest of ,madeira indicate that a low topographic feature which might be called the ,madeira ,rise continues into the northeast part of the area shown as ,madeira ,abyssal ,plain4 ,this abyssal plain is thus somewhat smaller than indicated in the drawings4 ,two ,,pdr records from this rise area are illustrated 7,pl4 #ac1 figs4 #a1 #b74 ,since the limits of the ,madeira ,abyssal ,plain are based on only four sounding profiles1 future surveys will cause relatively great changes in this portion of the diagram4 ,,abyssal ,,hills ,definition and distribution4--,an abyssal hill is a small hill that rises from the ocean-basin floor and is from a few fathoms to a few hundred fathoms in height and from a few hundred feet to a few miles in width4 ,the term abyssal hills province is applied to those areas of the ocean-basin floor in which nearly the entire area is occupied by hills--that is1 the province lies at approximately the depth of the adjacent abyssal plain but lacks a smooth floor4 ,isolated abyssal hills and groups of abyssal hills also occur in the abyssal plains4 ,illustration3 ,,figure #be4--;,index chart1 location of abyssal hills profiles illustrated in ,figures #bf and #bg ,limits of abyssal hills provinces shown by dotted lines4 ,illustration3 ,,figure #bf4--;,eleven profiles1 ,western ,atlantic ,abyssal ,hills ,province #dj3a vertical exaggeration2 positions shown on ,figure #be4 ,abyssal hills are found along the seaward margin of most abyssal plains and probably occur in profusion in basins isolated from adjacent land areas by ridges1 rises1 or trenches4 ,in the ,north ,atlantic the abyssal hills form two strips parallel to the ,mid-,atlantic ,ridge for virtually its entire length4 ,the ,bermuda ,rise is bordered on the southeast by abyssal hills which join with the strips adjoining the ,mid-,atlantic ,ridge 7,fig4 #be74 ,southeast of the ,bermuda ,rise the abyssal plain is absent1 and consequently the ,western ,atlantic ,abyssal-,hills ,province exceeds #ejj miles in width4 ,illustration3 ,,figure #bg4--;,eight profiles1 ,eastern ,atlantic ,abyssal ,hills ,province ,vertical exaggeration #dj3a2 positions shown on ,figure #be4 ,in the ,north ,atlantic the axes of maximum depth on the eastern and on the western sides of the ,mid-,atlantic ,ridge lie in the abyssal-hills province4 ,this pattern probably continues through the ,south ,atlantic1 ,indian ,ocean1 and ,south ,pacific oceans4 ,individual abyssal hills are identical to the smaller hills which rise from the steps of the ,mid-,atlantic ,ridge and are probably of the same origin4 ,the abyssal hills and the ,lower ,step of the ,mid-,atlantic ,ridge can be distinguished topographically only by the contrast in level4 ,regional description4--,the abyssal hills within the area of the physiographic diagram are illustrated by profiles ,,wh-#a-aa and ,,eh-#a-h reproduced in ,figures #bf and #bg respectively4 ,,western ,,atlantic3 ,the abyssal-hills province ranges from a few miles to more than #abe miles in width from the north edge of the map to the ,southeast ,newfoundland ,ridge4 ,along profile ,,wh-#a the province consists of about a dozen hills #c-d miles wide and #ej-ajj fathoms high1 while in ,,wh-#b the hills are #d-aj miles in width1 and some exceed #bjj fathoms in height4 ,the abyssal-hills province appears to pinch out at the ,southeast ,newfoundland ,ridge4 ,southwest of the ,southeast ,newfoundland ,ridge the abyssal hills form a belt #fj-abj miles wide which skirts along the north edge of ,corner ,rise4 ,in this area1 as illustrated by ,,wh-#c1 -#d1 and -#e1 the largest abyssal hills nowhere exceed #bej fathoms in height4 ,the individual hills range from #c to #ab miles wide2 maximum depths between individual hills frequently exceed the depth of the adjacent abyssal plain by #ej-ajj fathoms4 ,along the northwest corner of ,corner ,rise the abyssal-hills province pinches out4 ,south of ,corner ,rise the province appears on both the east and the west sides of the ,sohm ,abyssal ,plain1 and isolated abyssal hills become more numerous within the abyssal plain4 ,in profile ,,wh-#f the abyssal hills within the province reach #cjj fathoms in height and are #c-e miles wide4 ,a few higher peaks occur such as the two in profile ,,wh-#f1 one #ejj fathoms high and #bj miles wide and the other #gjj fathoms high and #ae miles wide4 ,in addition eight isolated hills #ajj to #age fathoms high rise from the plain in the same profile4 ,to the south1 the frequency of hills within the plain increases1 and the hills province widens4 ,in profile ,,wh-#g the province increases to #ce miles in width on the east side of the ,sohm ,plain and to #ajj miles in width on the west side4 ,the smaller individual hills in the plain are #bjj fathoms high1 in contrast to the average of #ajj fathoms in ,,wh-#f4 ,twenty-one individual hills rise from the plain in ,,wh-#g1 in contrast to #ae in ,,wh-#f4 ,in ,,wh-#h the abyssal plain is represented by a flat-floored valley only #ab miles wide2 the remaining #ejj-mile width of the abyssal floor is occupied by abyssal hills4 ,individual hills are #cjj to #fjj fathoms high and #e to #aj miles wide 7,fig4 #bh2 ,pl4 #aj74 ,if we filled all the depressions on ,,wh-#h with #ajj fathoms of sediments the profile would closely resemble ,,wh-#g4 ,illustration3 ,,figure #bh4--,tracing of ,,pdr record1 abyssal hills1 southeast of ,bermuda ,rise ,,wh-#i and ,,wh-#aj are very similar to ,,wh-#h except that individual hills seem to become broader and lower toward the south4 ,the height of individual hills in ,,wh-#aj ranges from #ajj to #bej fathoms4 ,south of ,,wh-#h the abyssal-hill province splits into two strips which border the ,nares ,abyssal ,plain4 ,the western strip lies below the eastern scarp of the ,bermuda ,rise ,scarp ,zone1 and the eastern strip follows the ,mid-,atlantic ,ridge1 sending a narrow strip westward along the northern edge of the outer ridge north of ,puerto ,rico4 ,a number of hills #ej fathoms high and #b-e miles wide are scattered over the eastern part of the ,nares ,abyssal ,plain4 ,abyssal hills are rare in the abyssal plain west of #fe ,w4 ,the abyssal-hill province along the southwestern ,bermuda ,rise is extremely narrow and intermittent4 ,no abyssal hills have been recorded for the ,hatteras ,abyssal ,plain1 and only locally is the province developed along the western side of the ,bermuda ,rise4 ,locally abyssal hills are moderately well developed along the northern margin of the ,bermuda ,rise4 ,,eastern ,,atlantic3 ,the abyssal floor west of the ,anglo-,french shelf is extremely narrow2 the abyssal plain and abyssal hills combined are only #hj miles wide4 ,the abyssal-hills province is absent1 but1 as shown on ,,eh-#a and ,,eh-#b 7,fig4 #bg71 large hills rise from the seaward edge of the ,biscay ,abyssal ,plain4 ,these hills are #e-aj miles wide and #ajj-djj fathoms high4 ,west of the ,iberia ,abyssal ,plain 7,,eh-#c7 the abyssal-hills province is wider and better developed than near the ,biscay ,abyssal ,plain4 ,south of ,gibraltar the abyssal floor widens southward2 northwest of ,cape ,verde it is more than #bjj miles wide4 ,profile ,,eh-#f runs obliquely through the province and indicates an exaggerated width for the province4 ,individual hills are #e-aj miles wide and #ajj-fjj fathoms high 7,pl4 #i1 fig4 #d74 ,the abyssal-hills province is widest1 and the hills are the highest where the depth is greatest1 a relation similar to that observed on the opposite side of the ,mid-,atlantic ,ridge in the sector southeast of the ,bermuda ,rise4 99 99 99 99 99 ,origin of abyssal-hills topography4--,the topography of the abyssal hills is considered to represent the original surface buried beneath the abyssal plains and perhaps beneath the continental rise4 ,this explanation agrees well with the smooth topography and the distribution of deep-sea sands in the abyssal plain4 ,the origin of the hills topography is a more difficult problem4 ,we have no rock samples from these provinces4 ,individual hills cannot be studied with present seismic-refraction techniques2 they do not seem to have a characteristic magnetic anomaly2 and ,worzel has only recently developed a method of gravity measurement which can be applied to a feature as small as an abyssal hill4 ,at present we have only topography as a basis of speculation of their origin4 ,as far as we know1 individual abyssal hills are not discernibly different from the smaller hills of the steps of the ,mid-,atlantic ,ridge or much of the topography of the oceanic rises1 and thus there is no reason to assume that the abyssal hills have a different origin4 ,we have noted that abyssal hills range from #ej to #fjj fathoms in height and with some exceptions from #d to #aj miles in width4 ,however1 many of the hills are about #bjj fathoms high and #e miles wide4 ,the hills are very steep-sided1 and frequently the sounder simply records a series of highlights from a succession of peaks 7,pl4 #aj2 ,pl4 #i1 fig4 #d74 ,soundings are difficult to obtain in the abyssal-hills provinces because of the great depth and primarily the preponderance of steep slopes 7,pl4 #aj74 ,we do not know whether individual hills are conical or elongate or1 in fact1 if they run in narrow1 sinuous ridges as suggested by ,tolstoy 7#aiea74 ,accurate1 detailed mapping of portions of the abyssal-hills provinces on scales of approximately #a3bj1jjj or larger should provide additional limits on theories of origin4 ,at present we cannot decide among vulcanism1 faulting1 or folding1 although folding seems the least probable4 ,,other ,,major ,,features ,,of ,,the ,,abyssal ,,floor ,abyssal gaps4--,if two adjacent but distinct abyssal plains have no through passage at or below the level of the higher plain1 they are said to be separated by a sill1 a ridge1 or a rise1 depending on the dimensions of the feature involved4 ,however1 several plains are connected by constricted passages4 ,an abyssal gap is a constricted passage connecting two abyssal plains which1 in the vicinity of the gap1 lie at different levels4 ,the sea floor slopes down continuously through the gap from the higher to the lower abyssal plain1 at a gradient considerably greater than that of either adjacent abyssal plain4 ,prominent abyssal gaps are known in the western ,north ,atlantic 7,vema ,gap7 and in the eastern ,north ,atlantic 7,theta ,gap74 ,an abyssal gap connects the ,colombia and ,venezuela abyssal plains of the ,caribbean4 99 99 99 99 99 ,mid-ocean canyons4--,whereas most submarine canyons are furrows cut into the continental-margin provinces1 a class of canyon is found in the abyssal plains1 generally associated with abyssal gaps4 ,a mid-ocean canyon is a steep-walled1 flat-floored persistent linear depression1 #a-e miles wide and a few to more than #ajj fathoms deep1 which occurs in an abyssal plain4 ,each mid-ocean canyon discovered in the ,north ,atlantic leads to an abyssal gap in a manner which suggests a genetic relationship4 ,all recognized mid-ocean canyons parallel the adjacent continental margin4 ,although all slope downward continuously they cut across the regional slope of the abyssal plain4 ,mid-ocean canyons or features resembling them have been found in the ,indian ,ocean ,bay of ,bengal 7,dietz1 #aiec71 in the northwest ,atlantic 7,ewing et al41 #aiec71 the western ,atlantic1 and the equatorial ,atlantic 7,beckmann1 in preparation74 ,gibson 7#aieh7 has reported one in the ,gulf of ,alaska4 ,three in the ,atlantic and one in the ,gulf of ,alaska have been mapped4 ,although mid-ocean canyons probably join with continental-margin submarine canyons1 no such connection has been mapped4 ,menard 7#aiee7 has recorded from the ,north ,pacific several crossings of features resembling the mid-ocean canyons of the ,atlantic1 which he refers to as deep-sea channels4 99 99 99 99 99 ,regional description4--,abyssal gaps and mid-ocean canyons are found in both the western ,atlantic and eastern ,atlantic4 ,illustration3 ,,figure #bi4--,northwest ,atlantic ,mid-,ocean ,canyon ,surveyed positions and extensions2 generalized bathymetry simplified from ,smith1 ,soule1 and ,mosby 7#aicg7 ,illustration3 ,,figure #cj4--;,eight east-west profiles showing ,northwest ,atlantic ,mid-,ocean ,canyon ,soundings obtained with ,,nmc sounder run with precision controlled ac power in #aidi ,illustration3 ,,figure #ca4--;,forty-eight cross sections of ,northwest ,atlantic ,mid-,ocean ,canyon ,soundings originally recorded on ,,uqn-#a;,b sounder with precision controlled ac power in #aieb ,illustration ,,western ,,atlantic3 ,the major abyssal plains of the western ,atlantic are connected from north to south by a series of abyssal gaps and mid-ocean canyons4 ,the ,northwest ,atlantic ,mid-,ocean ,canyon 7,fig4 #bi7 begins in an unknown area north of the limit of the physiographic diagram 7,ewing et al41 #aiec74 ,it runs south parallel to the continental margin of the ,grand ,banks on the west and to the ,mid-,atlantic ,ridge on the east until it reaches the ,southeast ,newfoundland ,ridge1 where it cuts through a narrow abyssal gap4 ,after passing through the gap1 the canyon turns west1 broadens1 and is finally lost in the ,sohm ,abyssal ,plain4 ,the mid-ocean canyon is about #c miles wide and #ej fathoms deep north of the ,southeast ,newfoundland ,ridge 7,fig4 #cj74 ,the west wall is about #aj-ae fathoms higher than the east wall 7,fig4 #cb74 ,the canyon has been mapped by more than #hj echo-sounding profiles 7,fig4 #ca74 ,the average slope of the sea floor at right angles to the axis of the canyon in most places exceeds the gradient of the canyon4 ,the gradient west to east is about #a3aejj1 while the gradient of the canyon from north to south is #a3bbej4 ,illustration3 ,,figure #cb4--,long profile of ,northwest ,atlantic ,mid-,ocean ,canyon ,numerals ,i-,,viii indicate location of profiles of ,figure #cj4 ,the mid-ocean canyon forms gentle meanders 7,fig4 #bi74 ,as the gradient of the canyon decreases1 the canyon changes its cross-section form from a narrow1 deep canyon to a broad1 shallow one 7,figs4 #ca and #cb74 ,the mid-ocean canyon follows an exceptionally narrow and deep abyssal gap through the ,southeast ,newfoundland ,ridge4 ,at its narrowest point the gap is no wider than the mid-ocean canyon4 ,mid-,ocean ,canyon ,no4 #b is nearly identical to the ,northwest ,atlantic ,mid-,ocean ,canyon in shape and form 7,pl4 #ad1 fig4 #b74 ,it has been traced for only #cej miles through the northwest arm of the ,sohm ,abyssal ,plain4 ,there is a strong suggestion of a low sill running northeast of the ,bermuda ,rise toward the tail of the ,grand ,banks4 ,such a sill would cut off the northwest arm of the ,sohm ,abyssal ,plain4 ,mid-,ocean ,canyon ,no4 #b would in this case be associated with this abyssal gap connecting the higher northwest arm with the deeper central and southern parts of the ,sohm ,plain4 ,a large magnetic anomaly which crosses the plain at this point is possibly evidence of a buried ridge beneath the abyssal plain4 ,mid-,ocean ,canyon ,no4 #b has been traced from the vicinity of ,kelvin ,seamount eastward to the supposed sill4 ,as in the case of the ,northwest ,atlantic ,mid-,ocean ,canyon the gradient at right angles to the canyon axis generally exceeds the gradient of the canyon floor4 ,a systematic difference in depth between the two walls was not found in ,mid-,ocean ,canyon ,no4 #b4 ,a small area 7#hjjj square miles7 of abyssal hills lies between the northwest arm of the ,sohm ,abyssal ,plain and the northern edge of the ,hatteras ,abyssal ,plain4 ,although many sounding lines have been run through this area it is not yet clear whether this area is best referred to as an abyssal gap or a sill1 although the evidence seems to favor a gap4 ,the western end of the ,sohm ,plain seems to reach a smooth sill a few dozen miles east of ,caryn ,peak1 and the abyssal plain surrounding ,caryn ,peak1 at the mouth of the ,hudson ,canyon1 seems either to be isolated or to be connected with the ,hatteras ,abyssal ,plain to the south through an abyssal gap4 ,an abyssal gap may possibly connect ,sohm ,plain to the eastern end of the ,nares ,abyssal ,plain1 but in consideration of the eastward gradients of the ,nares ,abyssal ,plain it seems probable that no gaps cut all the way through the wide abyssal-hills province which separates the two plains4 ,the gap connecting the ,hatteras ,abyssal ,plain and the ,nares ,abyssal ,plain southwest of the ,bermuda ,rise has been named ,vema ,gap after the ,research ,vessel ,,vema which has been used most extensively in this area4 ,vema ,gap is about #bj miles wide and #gj miles long2 its long axis is oriented approximately west-east4 ,the ,hatteras ,plain reaches a depth of #bijj fathoms a few miles west of the gap4 ,the gradient of the plain is about #a3cjjj at that point4 ,the ,nares abyssal plain to the southeast lies at about #cjgj fathoms and slopes eastward with a gradient of about #a3cejj4 ,the floor of the gap1 in sharp contrast to the adjacent plains1 slopes eastward at an average gradient of #a3cjj4 ,the edge of the ,hatteras ,abyssal ,plain is cut by several mid-ocean canyons #bj fathoms deep and a mile wide which develop a few miles to the west and converge on the abyssal gap4 ,associated with ,vema ,gap is a large magnetic anomaly similar to the one observed near the supposed gap north of the ,bermuda ,rise1 which again could possibly be evidence of a prominent buried ridge forming the sill of the gap4 ,the ,old ,bahama ,channel ,abyssal ,plain and the ,hispaniola-,caicos ,abyssal ,plain are probably connected by a steep-walled abyssal gap which runs west to east south of ,great ,inagua ,island4 ,illustration3 ,,figure #cc4--,tracing of ,,pdr record across ,theta ,gap ,,eastern ,,atlantic3 ,the only abyssal gap known in the eastern ,atlantic was sounded by ,m_/,v ,,theta and is here named ,theta ,gap4 ,this gap lies off the northwest cape of ,spain between the ,biscay and ,iberia abyssal plains4 ,its existence is based on only a few profiles1 one of which is illustrated in ,figure #cc4 ,small depressions a few fathoms deep and #a-b miles wide were observed in the ,biscay ,abyssal ,plain and may represent mid-ocean canyons1 which may possibly connect with ,theta ,gap 7,pl4 #h1 fig4 #b74 ,insufficient precision-sounding tracks are available in this area to determine the exact nature of these features4 99 99 99 99 99 ,origin of abyssal-floor topography4--,the explanation that abyssal plains represent portions of the abyssal floor buried beneath sediments transported by turbidity currents1 and that the abyssal hills represent this unburied surface1 has been offered by ,heezen et al4 7#aiea2 #aied7 and by ,menard 7#aiee74 ,abyssal gaps are pictured as passages through which turbidity currents flow from a higher plain to a lower one4 ,sediment must have filled in the ,hatteras ,plain to the present depth of the western end of ,vema ,gap before the ,nares ,abyssal ,plain could begin to form4 ,ewing et al4 7#aiec7 suggest that the ,northwest ,atlantic ,mid-,ocean ,canyon was probably formed by turbidity currents which flow from the vicinity of ,greenland to the ,sohm ,abyssal ,plain4 ,whether the canyon-forming process was largely erosional or depositional remains to be seen1 but the narrow1 deep abyssal gap in the ,southeast ,newfoundland ,ridge suggests erosion4 ,the parallelism of the ,mid-,ocean ,canyon with the ,mid-,atlantic ,ridge even suggests a tectonic origin4 ,the deep-sea sands of the canyon floor and its continuous gradient argue as strongly for a turbidity-current origin4 ,the features of the smooth parts of the abyssal floor seem clearly the result of deposition by turbidity currents 7,ericson et al41 #aiee2 in press74 ,,oceanic ,,rises ,definition and distribution4--,an oceanic rise is a large area 7measured in hundreds of miles71 not connected to or included in a mid-oceanic ridge or connected to a continental rise1 which rises a few hundred fathoms above the surrounding abyssal floor4 ,the topography of an oceanic rise ranges from gentle to extremely rugged4 ,included in this classification is the ,bermuda ,rise and ,corner ,rise of the ,north ,atlantic1 the ,rio ,grande ,rise of the ,south ,atlantic1 and a number of similar but unnamed features in the ,indian and ,pacific oceans4 99 99 99 99 99 ,regional description4--,only three oceanic rises are situated in the ,north ,atlantic4 ,they are3 ,bermuda ,rise1 ,corner ,rise1 and ,rockall ,rise4 ,of these only the ,bermuda ,rise has been crossed by many echo-sounding traverses4 ,,bermuda ,,rise3 ,in the center of the ,north ,america ,basin and surrounding the island of ,bermuda is an oval asymmetrical arch about #cjj by #fjj miles with the long axis oriented northeast4 ,the topography of the ,bermuda ,rise is relatively gentle as compared to the ,mid-,atlantic ,ridge but considerably more rugged than the continental rise 7,pl4 #bg74 ,the rise is usually distinctly marked on the west by a #aj- to #ajj-;fathom decrease in depth and a change from the monotonously smooth abyssal plain on the west to gently rolling hills1 #bj-ej fathoms high and #b-aj miles wide 7,pl4 #af74 ,in contrast the eastern edge of the rise is marked by a series of scarps #cjj-ijj fathoms high 7,pl4 #ag71 and the adjacent rise topography is relatively rugged4 ,west of the scarp zone the topography is quite smooth to the western margin of the rise 7,pl4 #af74 ,an apron #cj miles wide surrounds the #bcjj-;fathom high pedestal which supports the island of ,bermuda 7,pl4 #bj74 ,from this apron ,ericson1 ,ewing1 and ,heezen 7#aieb71 reported quantities of shallow-water-derived carbonate clastics4 ,north of ,bermuda the rise is marked by a number of high seamounts which continue across the adjacent abyssal plain and form the ,kelvin ,group of seamounts4 ,many of these appear to be flat-topped4 ,the ,bermuda ,rise is bounded on the east and north by the ,sohm ,abyssal ,plain1 on the west by the ,hatteras ,plain1 and on the south by the ,nares ,plain4 ,for a short distance on the northwest and a few hundred miles on the southeast the rise is bordered by abyssal hills4 ,the western edge of the ,bermuda ,rise is formed in places by a scarp1 but particularly in the northwest the ,bermuda ,plateau seems to dip gently beneath the ,hatteras ,abyssal ,plain4 ,the details of the topography of the ,bermuda ,rise are demonstrated by the series of radiating profiles in ,plate #bg4 ,bermuda ,pedestal4--,the islands of ,bermuda lie along the southeast rim of a flat-topped pedestal whose surface lies less than #bj fathoms below sea level4 ,the sides of the ,bermuda ,pedestal slope at gradients of #a3e to #a3cj and fall rapidly to the #bcjj-;fathom contour where the base of the pedestal is reached4 ,the pedestal is #ej miles by #hj miles at its base4 ,cores containing ,tertiary sediments and recent reef detritus1 and in one case basaltic rock1 have been obtained from the sides of the ,bermuda ,pedestal 7,pl4 #bh74 ,bermuda ,apron4--,encircling the base of the ,bermuda ,pedestal is a smooth1 gently sloping apron or depositional terrace4 ,the width of the apron is irregular and ranges from #dj miles on the east to #bj miles on the west4 ,gradients decrease to #a3gjj away from the pedestal1 but the outer edge of the apron in places has gradients of #a3ij4 ,on some profiles hills up to #abe fathoms in height occur near the outer edge of the apron and become increasingly numerous until at a distance of #de miles from the pedestal the apron is not recognizable as a topographic feature4 ,the limits of the apron will ultimately be defined by a study of the sediments4 ,bermuda ,plateau4--,the ,bermuda ,plateau is an oval area of #ij1jjj square miles1 which lies roughly in the center of the ,bermuda ,rise4 ,the topography is characterized by low hills and rather extensive intermontane valleys 7,pl4 #af74 ,few individual hills exceed #ej fathoms in height4 ,the topography of the sub-province is well illustrated in ,plate #af4 ,the depth is #bdjj to #bgjj fathoms4 ,the plateau is bounded on the southeast by the ,bermuda ,scarp ,zone4 ,on the west it extends almost to the edge of the rise4 ,on the north the ,crescent ,peaks and ,muir ,seamount ,group have made it difficult to define the edge of the plateau4 ,crescent ,peaks4--,northwest of ,bermuda a crescent-shaped line of conical peaks borders the ,bermuda ,apron4 ,individual peaks are #fjj fathoms high and #d to #f miles wide at their base4 ,this range of peaks forms a distinct sub-province which rises from the ,bermuda ,plateau4 ,bermuda ,scarp ,zone4--,the ,bermuda ,plateau is broken along its eastern margin by a series of scarps 7,pl4 #ag74 ,there appear to be two systems of scarps1 one trending about ,n4 #ee ,w4 and the other about ,n4 #ce ,e4 ,individual scarps range from #ajj to #gjj fathoms in height4 ,the intersecting set of lines shown on the province chart 7,pl4 #bj7 indicates prominent scarps in this area4 ,dashed lines represent more speculative scarps4 ,a further study of this interesting area is underway1 and it is hoped that a more-detailed mapping of these scarps will be possible4 ,needless to say1 dredging on these scarps should bring rich rewards in fossil sediments and igneous rocks which are undoubtedly exposed on these precipitous cliffs4 ,the general character of the scarp zone is illustrated in ,plate #ag by an echogram4 ,there seem to be three or four major ne-sw scarps4 ,in the east-central ,bermuda ,rise the areas between the scarp zones remain at virtually the same depth as the unfractured ,bermuda ,rise farther west4 ,however1 toward the southeast the inter-scarp areas drop as a series of steps4 ,the depth along the base of each scarp is nevertheless deeper than the next lower step4 ,the smaller topographic features of the southeast part of the scarp zone are very similar to the abyssal hills to the southeast and are thus probably of the same origin4 ,the strips between successive scarps tend to shallow to the southeast and reach minimum depths just before the next scarp is reached4 ,muir ,seamount ,group4--,in #aide workers on the ,u4,s4,s4 ,,muir discovered a large seamount #adj miles northeast of the ,bermuda ,islands4 ,subsequent reconnaissance surveys by the ,lamont ,geological ,observatory 7,tolstoy1 #aiea2 ,tolstoy and ,ewing1 #aidi7 revealed that the peak was asymmetrical in east-west profile 7considerably steeper on the east7 and that the seamount was elongate northeast-southwest parallel to the axis of the ,bermuda ,rise4 ,cores taken near its summit contained ,eocene to ,pleistocene sediment4 ,additional seamounts have been discovered in the area by ,worzel and ,shurbet 7#aiee7 and ,northrop and ,frosch 7#aied74 ,the asymmetrical profile and the elongate shape parallel to the axis of the ,bermuda ,rise suggest that ,muir ,seamount is a tectonic uplift rather than a volcanic pile1 but admittedly undersea vulcanism need not always produce symmetrical cones4 ,as known1 ,muir ,seamount is #ce miles wide 7northwest-southeast71 #fj miles long 7northeast-southwest71 and rises #agjj fathoms above the ,bermuda ,rise4 ,the minimum sounding recorded is #hdf fathoms4 ,the ,muir ,seamount and near-by associated peaks apparently are not directly related to the ,kelvin ,seamount ,group farther north4 ,the north and northwest margin of the ,bermuda ,rise1 like that on the west1 is in some places a scarp and in other places a gentle transition4 ,near the northwest corner of the ,bermuda ,rise a range of hills each about #bj fathoms high and #c miles wide follows the margin of the rise for many miles4 ,the northeastern margin of the ,bermuda ,rise is abrupt in most places1 and in some places a single scarp #ejj fathoms high is all that separates the ,bermuda ,rise from the adjacent abyssal plain4 ,sediments of the ,bermuda ,rise4--,most of the ,bermuda ,rise lies below the depth of #bejj fathoms1 and thus the sediment ranges from foraminiferal clay through red clay with a predominance of red clay4 ,in the vicinity of the ,bermuda ,pedestal calcareous detrital sediments have built a depositional apron around the base of the pedestal in depths of #bcjj to #bdej fathoms 7,pl4 #bh74 ,the seamounts of the ,bermuda ,rise are rocky1 as shown by photographs and bottom samples4 ,several cores from the ,muir ,seamount revealed a variety of ,tertiary foraminiferal lutites4 ,with the exception of the detrital sediments of the ,bermuda ,apron1 the scoured crests and flanks of the larger seamounts1 and the steeper scarps1 the ,bermuda ,rise is covered preponderantly by pelagic sediments4 ,this is in sharp contrast to the surrounding abyssal plain and near-by continental rise1 where cores reveal frequent alterations of detrital and pelagic sediments 7,pl4 #bh74 ,,corner ,,rise3 ,much less extensive and less well known is ,corner ,rise which lies directly south of the ,grand ,banks on the east side of the ,sohm ,abyssal ,plain4 ,corner ,rise is so named because its northwest boundary with the abyssal floor forms a sharp1 nearly right-angled corner 7,pl4 #bj74 ,the main part of ,corner ,rise is formed by a group of large1 poorly surveyed seamounts4 ,several of the peaks rise to #aejj fathoms4 ,the area is represented in profile ,i of ,plate #bb 7between mile marks #ajjj and #abjj74 ,photographs taken on ,corner ,seamount at the northwestern extremity of ,corner ,rise showed rippled and hard-clay bottom to #abjj fathoms4 ,the fact that these seamounts apparently form a prolongation of the ,kelvin ,seamount ,group suggests the need for detailed investigation of the latter seamounts and the probability that additional volcanic seamounts may be found along the same trend4 ,illustration3 ,,figure #cd4--,natural scale profile1 ,kelvin ,seamount ,group ,,rockall ,,rise3 ,southwest of ,rockall ,bank between #ai,w4 and #bc,w4 on the #ejth parallel1 rising from the abyssal floor of the northeastern ,atlantic1 is an ill-defined area of irregular topography which seems not to belong to the ,lower ,step of the ,mid-,atlantic ,ridge4 ,little is known of this area1 and its classification as a rise may not survive more detailed study4 ,the area is illustrated in ,plate #be by profile ,e-#a4 ,,seamounts ,,of ,,the ,,ocean-,,basin ,,floor ,a seamount is defined as any isolated elevation which rises more than #ejj fathoms above the sea floor4 ,those seamounts which lie entirely on oceanic rises have been described as part of the rise topography4 ,now we will describe the seamounts of the abyssal floor4 ,,kelvin ,,seamount ,,group3 ,an impressive row of large conical peaks runs from the vicinity of ,georges ,bank for #fjj miles toward the northeast tip of the ,bermuda ,rise4 ,a profile plotted at natural scale which crosses five of the largest seamounts is reproduced in ,figure #cd4 ,the line of seamounts runs across the continental rise1 abyssal plain1 and the ,bermuda ,rise1 seemingly little affected on crossing the province boundaries4 ,the larger seamounts such as ,kelvin ,seamount are about #bjjj fathoms higher than the adjacent plain and are as much as #ce miles in diameter at the base4 ,those which rise from the continental rise or the abyssal plain do so abruptly1 suggesting that their bases are partially buried4 ,the tops of most of these seamounts lie between #eej and #hej fathoms1 and at least a few are flat-topped4 ,they are thus very similar to the flat-topped guyots of the ,pacific in size1 shape1 and the range of depths of their flat summits 7,hamilton1 #aief74 ,photographs taken on these seamounts showed rock1 ripples and live solitary corals4 ,,caryn ,,seamount3 ,a small conical peak1 #ajjj fathoms high1 whose base is #h miles in diameter1 lies in the abyssal plain west of the ,bermuda ,rise 7#cf #de,n474 ,a magnetic survey of the peak has been published by ,miller and ,ewing 7#aief74 ,they found an exceptionally large anomaly associated with the peak1 which clearly showed its volcanic origin4 ,cores from the peak contained manganese nodules1 altered volcanic rocks1 and ,upper ,cretaceous to ,recent fossils1 which shows that it is at least as old as ,upper ,cretaceous4 ,the base of the peak rises from the abyssal plain which extends out from the ,hudson ,submarine ,delta4 ,,horseshoe ,,seamount ,,group3 ,about #cjj miles due west from the ,straits of ,gibraltar an impressive group of seamounts lies in a horseshoe-shaped arc4 ,several of these1 most notably ,ampere and ,josephine seamounts1 rise to less than #ajj fathoms4 ,josephine ,seamount is the largest of the group and lies along an east-west topographic trend 7the ,azores-,gibraltar ,ridge74 ,in the southern half of the ,horseshoe ,group the individual seamounts appear to be coalescing cones similar to the seamounts of the ,kelvin ,group4 ,seamounts of the northern half1 although imperfectly known1 seem to be elongated east-west4 ,the southern half of the group appears to resemble volcanic cones1 while in the northern half tectonic deformation seems to have played a larger part4 ,the seamounts have been cored1 dredged1 and photographed by a ,lamont ,observatory expedition4 ,the sediments obtained from the seamounts are middle ,tertiary to ,recent 7,sutton et al41 #aieg74 ,illustration3 ,heezen et al41 ,,pl4 #af ,,figure #a4 ,,western ,,bermuda ,,rise ,,figure #b4 ,,central ,,bermuda ,,rise ,,figure #c4 ,,east-,,central ,,bermuda ,,rise ,,figure #d4 ,,eastern ,,bermuda ,,rise ,,representative ,,pdr ,,records ,,from ,,bermuda ,,rise ,depth in fathoms4 ,illustration3 ,heezen et al41 ,,pl4 #ag ,,pdr ,,record1 ,,bermuda ,,scarp ,,zone ,depth in fathoms4 ,illustration3 ,heezen et al41 ,,pl4 #ah ,,figure #a4 ,,high ,,fractured ,,plateau ,,figure #b4 ,,upper ,,step ,,pdr ,,records ,,mid-,,atlantic ,,ridge ,depth in fathoms4 ,illustration3 ,heezen et al41 ,,pl4 #ai ,area of each photograph is about #f by #h feet4 ,,plate #ai4--,,ocean-,,bottom ,,photographs2 ,,mid-,,atlantic ,,ridge ,,figure #a4 7,station ,t#a-i1 photo #db7 ,depth #adaj fathoms1 location #dh #ch,n41 #bh #dh,w41 on ,western ,rift ,mountains1 ,mid-,atlantic ,ridge4 ,in this plate ,figures #a1 #b1 and #c are closely spaced photographs less than #ajj feet apart4 ,note the coarse-grained light and dark gravel in winnow row in the foreground and the light-colored clay or ooze bottom in background4 ,of the sixty photographs taken at this location three resembled ,figures #b and #c1 several resembled ,figure #a1 and in the remainder the ocean floor was composed entirely of the light and dark gravel4 ,,figure #b4 7,station ,t#a-i1 photo #dc7 ,location about #ej feet from photo shown in ,figure #a1 same depth and position4 ,the dark color of the rocks may be due to a coating of manganese dioxide4 ,however1 the rocks may actually be composed of dark material2 no dredgings were taken here4 ,all dredgings from ,mid-,atlantic ,ridge have brought up basalt and in some cases also gabbroic and serpentinized rock4 ,it seems likely that the rock in ,figure #b and #c of this plate is basalt4 ,note the abundance of sessile life on the rocky areas in contrast to its absence in the gravel-covered areas4 ,,figure #c4 7,station ,t#a-i1 photo #de7 ,location about #ajj feet from photo shown in ,figure #b1 same depth and position4 ,rock bottom on the ,western ,rift ,mountains1 ,mid-,atlantic ,ridge4 ,,figure #d4 7,station ,v#d-g1 photo #bg7 ,depth #ejj fathoms1 location #cg #be,n41 #ca #aj,w41 ,western ,rift ,mountains1 ,mid-,atlantic ,ridge1 south of the ,azores ,plateau4 ,,figure #e4 7,station ,t#a-ed1 photo #ae7 ,depth #bajj fathoms1 location #bc #jg,n41 #dc #de,w41 ,upper ,step 7eastern side71 ,mid-,atlantic ,ridge4 ,apparatus in lower right attached to camera4 ,note tracks of crawling animal in left side of photo and small holes in bottom sediment4 ,photograph contrasts sharply with those from ,rift ,mountains in lack of current or oscillation ripples and rock outcrops4 ,,figure #f4 7,station ,t#a-ad1 photo #f7 ,depth #bacj fathoms1 location #df #jd,n41 #ag #dc,w41 ,lower ,step 7eastern side71 ,mid-,atlantic ,ridge4 ,note fecal pellets1 mounds1 and small holes4 ,again lack of evidence of strong currents or outcrops is notable4 ,positions of stations shown on ,plate #cj ,photographs of the seamounts generally show winnowed and rippled sediment and rock 7,pl4 #ae74 ,virtually all loose sediment is being removed from the seamounts4 ,the horseshoe1 open to the east1 encloses an abyssal plain which is1 judging from the sea-floor gradients1 fed largely from the east by turbidity currents originating in the ,straits of ,gibraltar and the ,gulf of ,cadiz areas4 ,,milne ,,seamount3 ,early charts of the western ,atlantic showed an extensive bank of #bj1jjj square miles rising from the center of ,newfoundland ,abyssal ,plain4 ,at about the center of this area an exceptionally high peak has been discovered by cable ships1 and the old name ,milne ,seamount has been assigned to this peak4 ,it rises more than #bejj fathoms above the abyssal floor4 ,two seamounts of similar size have been found north and south of the ,milne ,seamount by workers on the ,r4 ,v4 ,,atlantis 7,fig4 #cj74 ,as the abyssal floor is better surveyed many more isolated seamounts will undoubtedly be discovered1 and they may reveal tectonically significant patterns4 ,,seismicity ,,of ,,the ,,ocean-,,basin ,,floor ,the ocean-basin floor provinces are virtually devoid of earthquakes of a size detectable at distant seismic observatories4 ,of course small earthquakes 7 #e1 ,richter scale7 would probably not be locatable in such remote regions4 ,the virtual absence of larger shocks makes it improbable that many small ones occur there either4 ,two earthquakes have occurred in the ,bermuda ,rise1 one near the west boundary and one in the scarp zone of the southeast ,bermuda ,rise 7,pl4 #bi74 ,several quakes were felt in ,bermuda before instrumental recording was available to permit location of their epicenters4 ,two quakes occurred in the abyssal plain northwest of the ,cape ,verde ,islands1 and two were located near ,theta ,gap northwest of ,cape ,finistere4 ,all other earthquakes of the central part of the ocean basin are associated with the ,mid-,atlantic ,ridge or its eastern extension4 ,,ocean-,,basin ,,floor ,,provinces ,,and ,,crustal ,,structure ,the results of seismic-refraction measurements in the ocean-basin floor can be divided into two categories depending on whether the measurements were made 7#a7 in the abyssal floor1 or 7#b7 on an oceanic rise4 ,measurements in the abyssal floor of the western ,atlantic 7,ewing1 ,sutton1 and ,officer1 #aied7 revealed the simple pattern shown in ,figure #ce;b and e--namely1 that beneath #d-e km of water lies 4#e-a km of sediments and sedimentary rock with a compressional-wave velocity of about #b km_/sec1 overlying #c-d km of oceanic crustal rocks 7#f4e km_/sec72 beneath this the sub-,m mantle rocks show a velocity of about #h4a km_/sec4 ,this pattern has been observed by most workers in the abyssal floors of other oceans 7,raitt1 #aieg2 ,hill1 #aief74 ,officer1 ,ewing1 and ,wuenschel 7#aieb7 and ,katz and ,ewing 7#aiee7 have reported on the structure of the ,bermuda ,rise4 ,the topographic change from abyssal floor to the ,bermuda ,rise is accompanied by a corresponding change in crustal structure 7,fig4 #ce;b and d74 ,a typical column measured on the ,bermuda ,plateau is shown in ,figure #ce;d4 ,here the sub-,m velocity appears to be lower1 or possibly a new intermediate-velocity layer is inserted between the oceanic crust and the true mantle4 ,in the ,bermuda ,rise seismic velocities in the oceanic crust differ somewhat from the typical abyssal-floor values4 ,in the ,bermuda ,apron and adjacent parts of the ,bermuda ,plateau 7,fig4 #ce;c7 above the oceanic crust a thick 7up to #d km7 section of #d4e km_/sec velocity is found which has been quite reasonably identified as sedimentary and volcanic rocks4 ,seismic-reflection measurements in the smoother parts of the ocean-basin floor fall into two general groups4 ,reflection records from the oceanic rises generally show a succession of reflections which can be correlated for considerable distances4 ,reflection records from the abyssal plains in general show many reflections which are usually impossible to correlate even between adjacent shots4 ,this difference has been explained by ,ericson1 ,ewing1 and ,heezen 7#aieb7 in terms of the distribution of turbidity-current deposits4 ,in the abyssal plains relatively frequent turbidity flows have deposited an alternating sequence of clays and silts which return a great number of reflections to the reflection seismograph4 ,in contrast the rises receive only pelagic sedimentation1 and thus the layering of their sedimentary cover is simple and widespread since it relates to major changes in pelagic sedimentation of past geologic ages4 ,illustration3 ,,figure #ce4--;,crustal sections in various physiographic provinces1 determined by seismic-refraction measurements 7a74 ,eastern ,new ,york2 ,katz and ,ewing 7#aiee7 7b74 ,western ,sohm ,abyssal ,plain2 ,station ,a #agb-bh1 from ,katz and ,ewing 7#aiee7 7c74 ,bermuda ,apron2 ,station ,a #agb-bj from ,katz and ,ewing 7#aiee7 and ,officer et al4 7#aieb7 7d74 ,bermuda ,plateau2 ,station ,a #agb-ai1 from ,katz and ,ewing 7#aiee7 7e74 ,nares ,abyssal ,plain2 personal communication from ,j4 ,i4 ,ewing 7f74 ,mid-,atlantic ,ridge2 personal communication from ,j4 ,i4 ,ewing ,,mid-,,oceanic ,,ridge ,,definition ,the third basic subdivision of the oceanic depression is the ,mid-,oceanic ,ridge1 a continuous median ridge which runs the length of the ,north ,atlantic1 ,south ,atlantic1 ,indian and ,south ,pacific oceans1 for more than #dj1jjj miles 7,heezen and ,ewing1 in press74 ,in the center third of the physiographic diagram a short segment of this world-encircling ridge is represented4 ,,mid-,,atlantic ,,ridge ,one can find references to the ,mid-,atlantic ,ridge in the scientific literature dating back more than #hj years4 ,before the advent of the echo sounder the lateral limits of the ,mid-,atlantic ,ridge were very difficult to define1 and even now widely different definitions are used4 ,murray 7#aiab7 mentioned that the ridge lay in depths less than #bjjj fathoms but pointed out that locally on the ridge depths exceeded #bjjj fathoms4 ,the ,,meteor expedition charts and profiles generally imply by their labeling that the ridge is the area enclosed by the #djjj-meter contour 7#bbej fathoms74 ,shepard 7#aidh7 states that its average depth is about #aejj fathoms1 but it rises about #ajjj fathoms above deeper zones on either side4 ,tolstoy and ,ewing 7#aidi7 and ,tolstoy 7#aiea7 in general limit the ridge to depths of less than #bejj fathoms1 although in one part of the text ,tolstoy and ,ewing limit it to less than #bbdj fathoms1 and ,tolstoy 7#aiea7 implies that the ridge extends to #bijj fathoms4 ,in the present paper the ,mid-,atlantic ,ridge is considered as a morpho-tectonic unit defined in terms of morphology1 and therefore its definition is not based on a closed isobath4 ,the ,mid-,atlantic ,ridge is that portion of the ,mid-,oceanic ,ridge system which lies within the limits of the ,atlantic ,ocean4 ,it consists of a broad1 fractured median arch or swell which occupies approximately the center third of the ocean4 ,its crest lies near the median line of the ocean1 and its lateral boundaries are formed by scarps#b which lie near the axes of maximum depth of the eastern and western basins4 ,adjacent to the ,mid-,atlantic ,ridge both to the east and to the west is the abyssal floor 7usually abyssal hills7 of the ocean-basin floor4 #b ,scarps have been seen on every recorded crossing4 ,if they should be absent on a future crossing1 it is expected that a major change in gradient will be found which will serve as a consistent definition for the ridge boundary4 ,exaggerated profiles are useful in bringing out the major morphological characteristics of deep-sea topography4 ,for some purposes1 however1 it is desirable to study the topography in profiles with no vertical exaggeration4 ,two such profiles are shown in ,figures #cg-da4 ,the position of the two profiles is indicated in ,figure #cf4 ,a very good idea of the individual slopes can be gained from a study of these natural-scale profiles1 but the province boundaries are very difficult to identify4 ,a typical cross profile at #dj3a exaggeration is shown in ,figure #db1 a typical oceanic cross section1 in which each physiographic province of the ,mid-,atlantic ,ridge is labelled4 ,illustration3 ,,figure #cf4--;,index to natural-scale ,mid-,atlantic ,ridge profiles reproduced in ,figures #cg-da ,,provinces ,,of ,,the ,,mid-,,atlantic ,,ridge ,the ,mid-,atlantic ,ridge was subdivided by ,tolstoy and ,ewing 7#aidi7 and ,tolstoy 7#aiea7 into 7a7 the central backbone or main range which is shallower than #afjj fathoms1 and 7b7 the flanks or the terraced zone between the #afjj- and #bejj-;fathom isobaths4 ,in this paper we use a similar but somewhat differently defined system by dividing the provinces of the ,mid-,atlantic ,ridge into two categories3 7#a7 the crest provinces1 and 7#b7 the flank provinces4 99 99 99 99 99 ,crest provinces4--,the provinces of the crest of the ,mid-,atlantic ,ridge consist of 7#a7 the ,rift ,valley 7or ,valleys72 7#b7 ,rift ,mountains2 and 7#c7 ,high ,fractured ,plateau 7,fig4 #dc74 ,the ,azores ,plateau1 which forms part of the crest1 presents additional problems and is discussed separately4 ,,rift ,,valley3 ,the most striking feature on an average profile across the ,mid-,atlantic ,ridge is a deep notch or cleft in the crest of the ridge4 ,in a small percentage of the sounding profiles two or three such valleys are present1 and on a few profiles no notable depressions are observed4 ,on an average profile the floor of the valley lies at about #bjjj fathoms1 while the adjacent peaks average about #ajjj fathoms below the sea surface4 ,the width of the valley between the crests of the adjacent peaks ranges between #ae and #cj miles1 and the depth of the valley floor beneath the highest adjacent peak ranges from #gjj to #bajj fathoms4 ,the width of the valley #ejj fathoms above its floor ranges from #e to #bb miles4 ,the range in observed depths of the valley is #aaej to #bhej fathoms in the area of the physiographic diagram4 ,the adjacent peaks range from #ejj to #acjj fathoms within the same area 7excluding the area near the ,azores7 7,fig4 #dg74 ,illustration3 ,,figure #cg4--,natural-scale ,mid-,atlantic ,ridge profile #a;,a ,slope corrections have been applied to profiles #a and #b4 ,the method is described by ,elmendorf and ,heezen 7#aieg74 ,illustration3 ,,figure #ch4--,natural-scale ,mid-,atlantic ,ridge profile #a;,b ,illustration3 ,,figure #ci4--,natural-scale ,mid-,atlantic ,ridge profile #a;,c ,illustration3 ,,figure #dj4--,natural-scale ,mid-,atlantic ,ridge profile #b;,a ,illustration3 ,,figure #da4--,natural-scale ,mid-,atlantic ,ridge profile #b;,b ,illustration3 ,,figure #db4--,type profile1 provinces of the ,mid-,atlantic ,ridge ,illustration3 ,,figure #dc4--,tracing of ,,pdr record1 ,rift ,valley1 ,rift ,mountains1 ,high ,fractured ,plateau1 and ,upper ,step ,illustration3 ,,figure #dd4--,tracing of ,,pdr record1 ,western ,rift ,mountains ,twenty-six crossings of the ,rift ,valley are shown in ,figure #de4 ,the profiles can be divided into three groups3 7#a7 single well-developed rift valley2 7#b7 several well-developed deep valleys2 7#c7 no particularly deep central valley4 ,most of the profiles 7#bj7 fall into the first class2 the second class is represented by #e1 and only #a falls in the third class4 ,the topography of the floor of the rift is rough4 ,in no instance has a flat floor been observed4 ,where the valley is widest mountains a few hundred fathoms high protrude from its floor4 ,,rift ,,mountains3 ,the steep walls flanking the rift each form one side of a large rough-sided block4 ,they might be considered as tilted blocks whose facing slopes form the ,rift ,valley4 ,the back or outer slope of the ,rift-,mountains ,province is generally broken into mountains as much as #ejj fathoms high and #aj miles wide 7,fig4 #dd74 ,the lateral limit of the ,rift-,mountains ,province is reached when the average slope of the sea floor flattens markedly4 ,because of the high local relief it is sometimes difficult to pick the boundary of the ,rift ,mountains1 but in almost all recorded profiles the approximate position of the boundary is unmistakable4 ,illustration3 ,,figure #de4--,twenty-six rift valley profiles1 ,mid-,atlantic ,ridge ,position of profiles shown on ,plate #bc ,illustration3 ,,figure #df4--;,five representative profiles1 crest and western flank of ,mid-,atlantic ,ridge ,,high ,,fractured ,,plateau3 ,the ,high ,fractured ,plateau is adjacent to the ,rift ,mountains on either side of the ridge 7,fig4 #db74 ,the local relief is about #djj fathoms from peak to adjacent valley1 and the distance from peak to peak ranges from #h to #bj miles4 ,in contrast to the adjacent flank provinces there are no filled intermontane valleys1 and the valleys are deeper and narrower than in the adjacent ,upper ,step ,province4 ,within the limits of the physiographic diagram1 the average depth of the ,high ,fractured ,plateau ranges from #aejj to #aijj fathoms4 99 99 99 99 99 ,flank provinces4--,between the outer margin of the ,high ,fractured ,plateau provinces and the level of the ocean-basin floor lies a succession of parallel provinces1 known as the ,upper ,step1 the ,middle ,step1 and the ,lower ,step4 ,the limits of these provinces are the least well defined of all the provinces described in this paper4 ,the flanks of the ridge are characterized by rough topography 7,pl4 #ah74 ,peaks of more than #bjj fathoms high occur at a frequency of about #ae per #ajj miles4 ,some of the valleys between peaks are smooth1 particularly in the provinces south of the ,azores ,plateau4 ,the flanks of the ,mid-,atlantic ,ridge are broken by scarps which seem to persist for relatively long distances parallel to the trend of the crest 7,pl4 #bj74 ,these scarps or scarp zones break the ridge into a succession of units here called steps 7,fig4 #df74 ,an alternative solution also seriously considered by the writers is that the steps might more correctly be considered as a series of tilted blocks which could be referred to as ramps4 ,the difference between the two solutions can be appreciated by inspecting ,figures #db and #df4 ,the writers must emphasize that the term terraces of ,tolstoy is in no sense the same as the term step used in this paper4 ,tolstoy defined his terraces as a succession of smooth shelves1 each from #a to #ej miles in width1 which occupy a zone #bjj-cjj miles wide4 ,features fitting this definition are called intermontane basins in this paper1 following a suggestion made by ,heezen et al4 7#aiea74 ,the location of smooth-floored intermontane basins is shown on ,plate #bj4 ,they are found only in the area extending about #h southwest of the ,azores4 ,small arrows indicate the slope of the smooth floors4 ,in general all the valleys slope away from the crest of the ridge4 ,steps1 on the contrary1 are a succession of average levels separated by scarps or scarp zones and in general are not smooth except that a few basins may be filled4 ,however1 this filling is limited to a small area south of the ,azores4 ,the flanks are divided into three steps3 upper1 middle1 and lower4 ,the division of anything into three parts is suspicious1 whether it be a geologic period or a physiographic region4 ,such divisions usually are later replaced as more information is obtained4 ,this is probably true of the three steps4 ,we are more confident of the significance of the boundaries shown on the province chart than of the uniqueness of the enclosed areas1 because each boundary marks a major scarp or scarp zone4 ,the steps are defined in part in any limited area on the basis of their mean depth4 ,in general the ,upper ,step ranges from #afej to #bcjj1 the ,middle ,step from #bbej to #bejj1 and the ,lower ,step from #bcej to #bhjj fathoms4 ,just as the maximum depth of the ridge and the axis of maximum depth of the basin vary with distance along the ridge 7or with latitude71 so the steps vary in depth and width 7,fig4 #dg74 ,illustration3 ,,figure #dg4--;,axial profile of the ,mid-,atlantic ,ridge 7a74 ,distance between province boundaries of the eastern and western flanks of the ,mid-,atlantic ,ridge measured along parallels of latitude4 7b74 ,width of the ,rift ,valley measured at #bej fathoms and at #ejj fathoms above the valley bottom and between the highest peaks of the ,eastern and the ,western ,rift ,mountains4 ,width in miles measured at right angles to the trend of the ridge4 7c74 ,the depth below sea level of the ,rift ,valley1 the ,rift ,mountains and the western and eastern axes of maximum depth4 ,the depths shown on this graph are in uncorrected echo-sounding fathoms4 99 99 99 99 99 ,azores ,plateau4--,the ,azores ,plateau is an area of #eb1jjj square miles of sea floor1 surrounding the ,azores ,islands1 where the depth is less than #ajjj fathoms4 ,the ,azores ,islands are oriented south-southeast-north-northwest along a topographic trend which strikes off toward the ,straits of ,gibraltar4 ,this topographic connection between the ,azores ,plateau and the southern ,iberian ,peninsula has been called the ,azores-,gibraltar ,ridge1 which the present writers consider as a poorly developed mid-oceanic ridge of the same general class as the ,mid-,atlantic ,ridge4 ,the ,azores ,plateau itself merges with the ,rift ,mountains of the ,mid-,atlantic ,ridge4 ,the sea-floor topographic trends of the eastern part of the plateau are parallel to the known tectonic and volcanic trends of the ,azores ,islands 7,agostinho1 #aicg74 ,in the western part of the ,azores ,plateau trends are north-south parallel to the main trends of the ,mid-,atlantic ,ridge4 ,although both ,wst 7#aidj;a7 and ,tolstoy 7#aiea7 have published contour charts of the ,azores ,plateau1 it remains largely a mystery whether the trends of the eastern ,azores ,plateau cross or join the axial trends of the ,mid-,atlantic ,ridge4 ,the ,azores ,plateau or bulge is generally considered as a highly fractured tectonic uplift in which vulcanism has played a comparatively small part 7,cloos1 #aici74 99 99 99 99 99 ,azores-,gibraltar ,ridge4--,an ill-defined irregular ridge runs from the eastern end of the ,azores ,plateau to the ,straits of ,gibraltar4 ,largely on the basis of its seismicity we infer that this ridge is structurally and topographically similar to the ,mid-,atlantic ,ridge4 ,the few existing topographic profiles across this feature suggest that the earthquake belt is associated with a rift valley of the same general type as the central ,rift ,valley of the ,mid-,atlantic ,ridge4 ,depths in this rift appear to reach #bcjj-bhjj fathoms1 and the depth of the tops of the adjoining mountains range from #afjj to #bjjj fathoms4 ,the flank provinces are even less well developed4 99 99 99 99 99 ,atlantis-,plato-,cruiser-,great ,meteor ,seamount ,chain4--,south of the ,azores a chain of great seamounts branches off from the ,high ,fractured ,plateau and crosses the ,upper and ,middle steps in a nearly north-south direction4 ,these seamounts--,atlantis1 ,plato1 ,cruiser1 and ,great ,meteor--in general have broad1 nearly flat summits at depths of #ajj-bej fathoms4 ,the largest one1 ,great ,meteor1 was discovered by workers on the ,,meteor in #aicg4 ,this seamount1 #fj miles across at its base1 rises majestically more than #bfjj fathoms above the floor of the ocean4 ,sands and calcareous rocks have been dredged from the summits1 and ,tertiary sediments have been obtained from the flanks of the seamounts4 ,photographs of the tops and of the flanks to a depth of #afjj fathoms show ripple marks4 ,this group is described in a paper by ,heezen1 ,ewing1 ,ericson1 and ,bentley 7in press74 ,,geology ,,and ,,geophysics ,,of ,,mid-,,atlantic ,,ridge ,,physiographic ,,provinces ,seismicity of the ,mid-,atlantic ,ridge4--,the earthquake epicenters instrumentally determined for the ,north ,atlantic up to #aief are shown in ,plate #bi4 ,nearly all earthquakes fall in the crest zone4 ,considering that determination of shocks is accurate only to within - to #a 1 it is quite surprising that the plotted epicenters form such a narrow belt4 ,investigation of the problem of the physiographic province most seismically active reveals that many epicenters actually plot in the ,rift ,valley and that virtually all that do not are within about #a of the ,rift ,valley4 ,all seismic activity therefore is limited to the crest provinces1 and probably virtually all the activity is concentrated within the ,rift-,valley ,province4 ,a line of epicenters runs from the ,rift ,valley near ,flores ,island of the ,azores toward the ,straits of ,gibraltar4 99 99 99 99 99 ,sediments and physiographic provinces of the ,mid-,atlantic ,ridge4--,the ,mid-,atlantic ,ridge is the major site of undisturbed pelagic sedimentation of the ,atlantic because of its isolation from down-slope movements starting on the continental margin4 ,however1 turbidity currents must form near the shores of oceanic islands and the edges of shallow banks and probably contribute sediments to the intermontane valleys4 ,photographs taken on the ,rift ,mountains and on the sides of major seamounts show scour marks and ripple marks1 indicating considerable winnowing and scour by deep-ocean currents 7,pl4 #ai74 ,this sediment carried from the tops of peaks and deposited on the steep mountain sides probably slumps occasionally and forms turbidity currents which flow to the adjacent valley floors 7,pl4 #bh74 ,for this reason cores taken in intermontane valleys and near the higher peaks will have considerable interlayering of turbidity-current deposits1 and much of the sides and crests of individual high mountains is bare rock4 ,in the ,rift ,mountains true pelagic sediments are only occasionally found4 ,it is striking to note that in coring and bottom photography bare-rock slopes are found most commonly in the ,rift ,mountains and ,high ,fractured ,plateau1 but flat-floored intermontane basins are absent in these provinces4 ,this must indicate either that the topography of the ,rift ,mountains is very new or that the sediment eroded from the crest provinces is carried all the way to the ,upper ,step ,province where it is deposited in the intermontane basins4 99 99 99 99 99 ,rocks of the ,mid-,atlantic ,ridge4--,our knowledge of the lithology of the ,mid-,atlantic ,ridge comes from three sources3 7#a7 rocks dredged from the sea floor1 7#b7 detrital rock fragments found in sediment cores1 and 7#c7 rocks exposed on the islands of the ,ridge4 ,some of the earliest rock dredging on the ,mid-,atlantic ,ridge was done in #ahhe by the ,,talisman expedition4 ,in #aidi ,furon 7#aidi7 reported the occurrence of fossil trilobites in dredge samples which had been stored for more than half a century in a ,french ,museum4 ,one dredging was made in the ,high ,fractured ,plateau of the eastern ,atlantic at #db #ba,n41 #ag #ab,w41 in #dbee meters depth 7#bccj fathoms74 ,furon believes that the material was in situ and therefore proof of early ,paleozoic outcrops on the ,mid-,atlantic ,ridge4 ,the abundant evidence of glacially rafted rocks even as far south as #cj ,n4 casts serious doubt on this conclusion1 but nevertheless the possibility that the material might have been in situ must be considered4 ,the ,mid-,atlantic ,ridge ,expedition of #aidg led by ,ewing made a number of successful rock-dredge hauls on the ,mid-,atlantic ,ridge4 ,the most successful hauls were made in the ,rift ,valley and on the adjacent ,rift ,mountains at about #cj ,n4 ,lat4 ,the specimens have been described by ,shand 7#aidi71 who reported olivine gabbro1 serpentine1 basalt1 and diabase4 ,one limestone of probably ,tertiary age was collected the same year but has not been described4 ,the suite of crystalline rocks obtained is similar to those found on oceanic islands elsewhere on the ,mid-,oceanic ,ridge4 99 99 99 99 99 ,crustal structure and the ,mid-,atlantic ,ridge provinces4--,the crustal structure of the ,mid-,atlantic ,ridge provinces has been determined at about #bj places by the seismic-refraction technique 7,fig4 #ce;f74 ,these studies1 conducted by ,john ,i4 ,ewing and ,w4 ,m4 ,ewing 7in press71 have shown that the average crustal structure of the crest provinces and ,upper ,step consists of #j4d km of low-velocity sediment and #b4h km of rock with a velocity of #e4a km_/sec overlying a substratum in which the velocity is #g4c km_/sec4 ,the thickness of the layer of low-velocity sediment varies considerably from place to place4 ,in the crest provinces the #e4a km_/sec layer is commonly exposed4 ,in the flank provinces appreciable thicknesses 7to #a km7 of sediment have been measured4 ,the sediment seems to thicken between major scarp zones and ridges as if the sediment were collecting in longitudinal basins parallel to the axis of the ridge4 ,an insufficient number of measurements have been made to determine whether these accumulations correlate with the boundaries of individual intermontane basins or with the limits of individual step provinces4 ,the structure of the abyssal floor1 crest provinces1 and flank provinces is compared in ,figure #ce4 ,the two higher-velocity layers shown in the abyssal-floor sections 7,nares and ,sohm ,abyssal ,plain1 ,fig4 #ce71 have been observed in all measurements made in these provinces4 ,the #f4g km_/sec layer is generally considered to be gabbroic1 and the #h4a km_/sec layer is by definition the earth's mantle4 ,in the ,mid-,atlantic ,ridge section the upper high-velocity material has an average velocity of #e4a km_/sec and is generally identified as basaltic rock4 ,the velocity of the underlying material 7#g4c km_/sec7 is intermediate between the velocity of oceanic crustal rocks 7#f4g km_/sec7 and that of mantle rocks 7#h4a km_/sec71 as observed both beneath the continents and beneath the abyssal floor4 ,ewing and ,ewing 7in press7 suggest that this intermediate velocity is the result of a physical mixture of oceanic crustal rocks and mantle rocks4 ,to explain such large-scale mixing they propose that extensive vulcanism and intrusion along the ,mid-,atlantic ,ridge have produced an intermingling of the crustal and mantle rocks1 and that this was associated with convection cells in the deep mantle which supply large quantities of basaltic magma and produce extensional forces on the crust and upper mantle4 ,nearly #bj crossings of the crest of the ridge have been made with the total-intensity magnetometer towed behind research vessels employing continuously recording echo sounders4 ,a characteristic anomaly pattern has been noted by ,ewing1 ,heezen1 and ,hirshman 7#aieg74 ,the ,rift ,valley is characterized by a large positive anomaly1 while the adjoining ,rift ,mountains show negative anomalies of #cjj to #ejj gammas 7,fig4 #dh74 ,free-air gravity anomalies over the crest provinces and ,upper ,step are usually #cj-ej mg positive1 while the ,rift ,valley as measured in two places gave free-air anomalies of -#c and -#bj mg4 ,illustration3 ,,figure #dh4--,profile of total magnetic intensity and topography1 ,mid-,atlantic ,ridge ,soundings made with ,,pdr4 ,magnetic measurements made with fluxgate total-intensity magnetometer4 ,magnetic values in gammas relative to an arbitrary zero4 ,illustration3 ,,figure #di4--,physiographic provinces and trans-,atlantic structure ,based on scattered seismic-refraction measurements in the ,north ,atlantic which have been projected along province boundaries4 ,the topographic profile was pieced together from continuously recorded echo-sounding profiles from ,new ,york to ,spanish ,sahara4 ,in the continental margin the upper layer represents the sedimentary rock4 ,the dashed symbol indicates the continental crustal rocks4 ,the lower layer represents oceanic crustal rocks4 ,the mantle lies below the lowest layer4 ,a heat-flow measurement by ,e4 ,c4 ,bullard in the ,rift ,valley province in the ,north ,atlantic indicated a value of about #g #aj cal4_/cm_/sec4 which is about #f times the average value of #a4b #aj cal4_/cm_/sec observed in the ,lower ,step and abyssal floor of the eastern ,atlantic 7,bullard1 #aied2 ,bullard et al41 #aief74 ,high heat-flow values have also been observed on the ,easter ,island ,ridge of the ,southeast ,pacific1 suggesting that the entire ,mid-,oceanic ,ridge rift system may be so characterized4 ,an adequate synthesis and explanation of all these converging lines of evidence has not yet been formulated4 ,however1 the correlation of so many types of geophysical and geological data speaks favorably for the validity and tectonic significance of the physiographic provinces described here4 ,on the basis of the observed correspondence of crustal structure and physiographic provinces a hypothetical trans-,atlantic structure section was prepared 7,fig4 #di74 ,seismic-refraction measurements were projected along province boundaries and plotted beneath an echo-sounding profile from ,new ,york to ,spanish ,sahara4 ,the black splotched areas represent the #g4c km_/sec layer4 ,this velocity intermediate between #h4a km_/sec of normal mantle and #f4g km_/sec of normal oceanic crust is considered 7#a7 a mixture of the two normal layers2 7#b7 a low-velocity part of the mantle1 or 7#c7 a distinct crustal layer characteristic of mid-oceanic ridges4 ,the structure shown for the continental margin of ,africa is based on analogy with the structure of the continental margin of northeastern ,united ,states4 ,this procedure seems justified by the close similarity of the continental-margin physiographic provinces of the two areas4 99 99 99 99 99 ,origin of the ,mid-,atlantic ,ridge4--,of the many theories which have been proposed for the origin of the ,mid-,atlantic ,ridge almost all have been extremely speculative1 and none has been based on any very detailed knowledge of the feature4 ,we are still a long way from having a comprehensive knowledge of the ,ridge4 ,the various theories of origin and their factual basis have been briefly reviewed by ,tolstoy and ,ewing1 who conclude that it is impossible to say if the feature is primarily of folded or faulted origin4 ,in a paper in press ,heezen and ,ewing compare in detail the topography and seismicity of the ,african rift valleys and the ,rift ,valley of the ,mid-,atlantic ,ridge4 ,their conclusion is that the two areas are of basically the same structure1 and in fact both form parts of the same continuous structural feature4 ,since the ,african rift valleys seem clearly to be the result of normal faulting resulting from extension of the crust1 ,heezen and ,ewing conclude that the topography of the ,mid-,atlantic ,ridge is largely the result of normal faulting4 ,whether the forces are the result of horizontal extension or vertical uplift remains the most important unsolved problem in connection with the origin of the continental as well as the suboceanic rift-valley systems4 ,hess 7#aied7 has proposed a mechanism relating suboceanic uplift to expansion due to serpentization of the upper mantle4 ,,sub-,,bottom ,,reflections ,,recorded ,,on ,,precision ,,depth ,,recorder ,,records ,,and ,,physiographic ,,provinces ,in some areas of the ocean ,,pdr records show a reflecting surface a few fathoms below the bottom4 ,such horizons are observed only when the sounder is operated with a short 7#e-millisecond7 ping length 7in echo sounding the transmitted sound is called the ping1 and its duration is called the ping length74 ,when a long ping is used the first returning echo masks any subsequent echoes occurring less than about #aj fathoms after the first echo4 ,to establish continuity of the lower horizon it is necessary to run the recorder without interruption1 sending pings once a second4 ,since a faulty pinging circuit or some accident of geometry could conceivably send out two closely spaced pings1 the supposed sub-bottom echoes must be carefully checked to make sure that they are not both bottom echoes from two closely spaced pings4 ,if two pings were being sent out the second echo would always symmetrically underlie the bottom surface4 ,if1 however1 the two surfaces show local variations1 it can be safely concluded that the deeper one is a true sub-bottom echo4 ,in order to observe sub-bottom echoes the sea floor should be reasonably smooth since in rugged relief side echoes and crossing highlight hyperbolas obscure any sub-bottom echoes which might occur4 ,sub-bottom echoes in the ,gulf of ,maine have been well described by ,murray 7#aidg74 ,in local inshore areas prominent sub-bottom echoes recorded by unmodified or slightly modified standard echo sounders have been used to map basement rocks 7,smith et al41 #aieb74 ,in the deep sea1 sub-bottom echoes or penetration are observed most frequently in the continental rise1 oceanic rises1 and the far edges of the abyssal plains4 ,penetration is rare on the open continental shelf and on the continental slope4 ,as the depth increases1 echoes are more difficult to obtain1 so that records from different depths cannot be directly compared in reference to ease of penetration4 ,it nevertheless seems to be true that sub-bottom echoes are rare or absent on ,,pdr records from the parts of the abyssal plains closest to the continental margin4 ,penetration in the continental rise is common but frequently irregular and intermittent4 ,one of the most persistent and uniform sub-bottom reflecting horizons observed occurs on the outer ridge east of the ,bahamas 7south of #cj ,n47 7,pl4 #f74 ,records from the abyssal plain immediately adjacent to the abyssal hills 7,pl4 #ac ,fig4 #d7 and from the flat-floored tongues in the abyssal hills 7,pl4 #aj7 reveal some of the deepest and strongest sub-bottom echoes4 ,good sub-bottom echoes are common in the ,bermuda ,plateau4 ,the sub-bottom reflecting layers frequently crop out1 and the overlying sediments thicken and thin1 revealing apparently noticeable variations in the rate of accumulation of sediments4 ,outcropping of sub-bottom layers on the steeper slopes indicate slumping1 while the deepening of the sub-bottom reflecting horizon in valleys indicates a greater rate of deposition4 ,high-frequency sound is normally strongly attenuated by transmission through sediments4 ,the observation of sub-bottom reflections with high-frequency sound pulses 7#ab kc7 indicates 7#a7 that the surface sediment is uniform and is of low density1 and 7#b7 that a fairly sharp density change occurs beneath this surface layer of low-density material4 ,in areas such as the outer ridge from #bb to #bi ,n4 ,lat4 and the southern ,bermuda ,rise1 it can be safely assumed that the upper layer consists of deep-sea red clay4 ,density measurements on red clay have indicated values of #a4be to #a4de4 ,the lack of sub-bottom reflections over the parts of the abyssal plains close to the continents is attributed to the numerous sand and silt layers found in the cores which reflect most of the sound4 ,the occurrence of good reflections beneath the outer edges of the abyssal plains could be explained by either assuming that for a long geologic time no sand-or silt-carrying turbidity current has reached this area1 or that red clay is deposited here much faster than elsewhere4 ,an extremely prominent sub-bottom reflector observed over a vast area of the east tropical ,pacific has been identified by coring with a #aj-;cm thick bed of white1 vitreous ash4 ,this suggests that sub-bottom reflections found elsewhere may1 in general1 represent ash horizons4 ,this1 of course1 would presuppose ash falls so vast that some record should have been preserved on land4 ,there is no reason to assume that there is but a single cause of deep-sea sub-bottom echoes4 ,the widespread occurrence of the sub-bottom interface on the deeper isolated rises may be of great importance if it be interpreted as evidence of a sudden change in sedimentation resulting in a change from higher- to lower-density sediment4 ,it is just conceivable1 however1 that some unstable diagenetic process may cause a sudden increase in compaction at a depth corresponding to the sub-bottom reflection4 ,the sub-bottom reflections in depths of #bfjj fathoms on the southern ,bermuda ,rise and the outer ridge is about 4#jb second after the bottom echo1 and this indicates a layer about #aj fathoms thick4 ,at a rate of deposition of #a cm_/#ajjj years this change in sediment type would have occurred #bj million years ago4 ,in a remotely situated oceanic area the factors controlling whether red clay or ,globigerina ooze is laid down are largely related to depth and temperature of the bottom water4 ,these two factors are related to those which control the solubility of the carbonate and thus the type of bottom deposit4 ,emiliani and ,edwards 7#aiec71 from a study of oxygen isotopes in benthic ,foraminifera in ,tertiary deep-sea sediments from the eastern ,pacific1 concluded that the temperature of ,pacific bottom water decreased #h ,c4 from the ,eocene to the present4 ,this should have caused a great increase in the solution of carbonate assuming other factors unchanged4 ,sub-bottom reflections then may also be interpreted as the result of a change in the temperature or the circulation of bottom water in the deep basin4 ,extensive1 basin-wide sub-bottom reflectors1 whether the result of vast beds of ash or widespread changes in pelagic sedimentation1 imply events of global importance4 ,the further investigation and identification of these reflectors should produce data of far-reaching application in geology1 climatology1 and paleo-oceanography4 ,,summary ,,of ,,province ,,characteristics ,the ,atlantic ,ocean floor consists of three major morphological divisions3 7#a7 continental margin1 7#b7 ocean-basin floor1 and 7#c7 ,mid-,oceanic ,ridge4 ,the continental margin is formed by three categories of provinces which represent 7#a7 the submerged continental platform1 7#b7 the steep edge of the continental block1 and 7#c7 the raised or depressed edge of the ocean floor4 ,the topographic detail of the continental margin is predominantly smooth except for the submarine canyons and minor irregularities of the upper continental rise4 ,a close correspondence of topography and distribution of recent sediments is apparent4 ,for example1 deep-sea sands are found in the submarine canyons and on the canyon deltas of the lower continental rise4 ,the continental slope appears to be a thinly veneered or bare outcrop of ,tertiary and ,mesozoic sediments4 ,individual topographic benches can be traced for many miles along the strike4 ,on the basis of published descriptions and dating of dredged rock1 certain prominent benches are identified as the outcrop pattern of various ,cretaceous and ,tertiary formations4 ,the lower continental rise can be directly traced into the outer ridge at ,cape ,hatteras4 ,the upper continental-rise and the marginal-trench provinces lie between the abrupt continental slope and the outer ridge4 ,seismic-refraction measurements in the continental margin indicate the greatest thickness of sedimentary rocks under the upper continental rise4 ,thus if we consider the initial form as an unfilled depression it would have been remarkably similar to the form of the present marginal trenches4 ,the ocean-basin floor lies between the continental margin and the ,mid-,oceanic ,ridge and consists of the deeper abyssal floor and the elevated oceanic rises4 ,on the abyssal floor adjacent to the continental margins are found the flattest surfaces of the earth4 ,these abyssal plains apparently were built by turbidity-current deposits4 ,the unburied abyssal floor is represented by the abyssal hills4 ,the oceanic rises are broad uplifts which rise from the abyssal floor through a series of scarps4 ,oceanic rises are covered with pelagic sediments except locally near islands and seamounts4 ,the crustal structure of oceanic rises differs significantly from the typical abyssal floor in having lower velocities and generally thicker crustal layers4 ,the ,mid-,oceanic ,ridge is a broad fractured arch whose axis follows the median line of the ocean4 ,it generally covers the center third of the ocean4 ,the ridge provinces are divided into crest provinces and flank provinces4 ,the crest provinces include 7#a7 the ,rift ,valley1 a long axial cleft #ae-cj miles wide and #ejj-aejj fathoms deep2 7#b7 the ,rift ,mountains which form the sides of the ,rift ,valley2 and 7#c7 the ,high ,fractured ,plateau1 a rugged plateau which borders the ,rift ,mountains4 ,the flank provinces consist1 on each side1 of roughly three steps separated by large scarps4 ,a seismic belt accurately follows the ,rift ,valley4 ,the topography of the ,mid-,oceanic ,ridge seems best explained by extensive normal faulting4 ,the mid-oceanic ,rift ,valley connects with and is probably of the same origin as the ,african rift valleys4 ,,bibliography ,,agostinho1 ,j41 #aicg1 ,volcanic activity in the ,azores3 ,bulletin ,volcanologique1 v4 ,,ii 7,series ,,ii71 p4 #chj-djj ,,andrade1 ,c4 ,f4 ,,de1 #aicg1 ,os vales ,submarinos ,portugueses3 ,servicos ,geologicos de ,portugal1 ,lisboa1 #bce p4 ,,anonymous1 #aice1 ,general bathymetric chart of the oceans1 ,sheet ,a#a3 ,information concerning the preparation of the third edition of ,sheet ,a#a2 ,north ,atlantic ,ocean3 ,int4 ,hydro4 ,bur41 ,spec4 ,pub4 #cj1 #cj p4 ---- #aici1 ,a summary of echo sounding apparatus3 ,int4 ,hydro4 ,bur41 ,monaco1 ,spec4 ,pub4 #cc1 #acg p4 ---- #aiec1 ,limits of oceans and seas3 ,intl4 ,hydro4 ,bur41 ,monaco1 ,spec4 ,pub4 #bc1 #bc p4 ,,armstrong1 ,j4 ,c41 #aiec1 ,oceanography in the ,tongue of the ,ocean1 ,bahamas1 ,b4,w4,i43 ,special ,report of the ,american ,museum of ,natural ,history1 ,n4 ,y41 #fc p4 ,,atwood1 ,w4 ,w41 #aidj1 ,the physiographic provinces of ,north ,america3 ,ginn and ,co41 ,boston1 #ecf p4 ,,bartholomew1 ,j4 ,c4 ,,son ,,ltd41 #aieb1 ,map of ,western ,europe1 scale #a3c1jjj1jjj3 ,edinburgh ,geographical ,inst41 ,edinburgh1 ,scotland ---- #aiee1 ,map of ,africa1 scale #a3aj1jjj1jjj3 ,edinburgh ,geographical ,inst41 ,edinburgh1 ,scotland ,,bentley1 ,c41 ,,and ,,worzel1 ,j4 ,l41 #aief1 ,geophysical investigations in the emerged and submerged ,atlantic coastal plain1 ,part ,x3 ,continental shelf1 slope and rise south of the ,grand ,banks3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fg1 p4 #a-ah ,,bourcart1 ,j41 #aidi1 ,geographie du fond des mers3 ,payot1 ,paris1 #cjg p4 ,,bourcart1 ,j41 and ,marie1 ,p41 #aiea1 ,sur la nature du ,rebord ,continental a l'ouest de la ,manche3 ,c4 ,r4 ,acad4 de ,science1 ,paris1 t4 #bcb1 p4 #bcdf-bcdh ,,bullard1 ,e4 ,c41 #aied1 ,the flow of heat through the floor of the ,atlantic ,ocean3 ,proc4 ,roy4 ,soc4 ,a1 v4 #bbb1 p4 #djh-dbi ,,bullard1 ,e4 ,c41 ,,and ,,gaskell1 ,t4 ,f41 #aida1 ,submarine seismic investigations3 ,proc4 ,roy4 ,soc4 ,a1 v4 #agg1 p4 #dgf-dii ,,bullard1 ,e4 ,c41 ,,maxwell1 ,a4 ,e41 ,,and ,,revelle1 ,r41 #aief1 ,heat flow through the ocean floor1 p4 #aec-agi in ,advances in geophysics3 v4 #c1 ,academic ,press1 ,n4 ,y41 #cbj p4 ,,cloos1 ,h41 #aici1 ,zur ,tektonik der ,azoren3 ,geol4 ,rundschau1 v4 #cj1 p4 #ejf-eaj ,,dahl1 ,w4 ,h41 #aibe1 ,tertiary fossils dredged off the northeastern coast of ,north ,america3 ,am4 ,jour4 ,sci41 #eth ser41 v4 #aj1 p4 #bae ,,davidson1 ,m4 ,j41 ,,and ,,miller1 ,e4 ,t41 #aief1 ,an airborne magnetic survey of the ,west ,indies1 ,gulf of ,mexico1 and the eastern ,united ,states continental margin 7,abstract73 ,am4 ,geophys4 ,union ,trans41 v4 #cg1 p4 #cda ,,day1 ,a4 ,a41 ,,hill1 ,m4 ,n41 ,,laughton1 ,a4 ,s41 ,,and ,,swallow1 ,j4 ,s41 #aief1 ,seismic prospecting in the western approaches of the ,english ,channel3 ,quart4 ,jour4 ,geol4 ,soc4 ,london1 v4 ,,cxii1 p4 #ae-dd ,,de ,,smitt1 ,v4 ,p41 #aicb1 ,earthquakes in the ,north ,atlantic as related to submarine cables 7,abstract73 ,am4 ,geophys4 ,union ,trans41 p4 #ajc-aji ,,dietrich1 ,g41 #aici1 ,einige ,morphologische ,ergebnisse der ,,meteor-,,fahrt1 ,januar bis ,mai #aich3 ,ann4 d4 ,hydrogr4 u4 ,marit4 ,meterol41 v4 #fg1 p4 #bj-bc ,,dietz1 ,r4 ,s41 #aieb1 ,geomorphic evolution of continental terrace 7continental shelf and slope73 ,amer4 ,assoc4 ,petrol4 ,geol4 ,bull41 v4 #cf1 p4 #ahjb-ahbj ---- #aiec1 ,possible deep-sea turbidity-current channels in the ,indian ,ocean3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fd1 p4 #cge-cgh ---- #aied1 ,methods of exploring the ocean floor1 p4 #aid-bjj in ,isaacs1 ,j4 ,d41 ,iselin1 ,c4 ,o',d41 ,editors1 ,oceanographic instrumentation3 ,natl4 ,acad4 of ,sci41 ,publ4 #cji1 ,washington1 ,d4 ,c4 ,,dietz1 ,r4 ,s41 ,,and ,,menard1 ,h4 ,w41 #aiea1 ,origin of abrupt change in slope at continental shelf margin3 ,amer4 ,assoc4 ,petrol4 ,geol4 ,bull41 v4 #ce1 p4 #aiid-bjaf ,,drake1 ,c4 ,l41 ,,sutton1 ,g41 ,,and ,,ewing1 ,m41 in press1 ,continental margins and geosynclines1 east coast of ,north ,america1 north of ,cape ,hatteras ,,drake1 ,c4 ,l41 ,,worzel1 ,j4 ,l41 and ,beckmann1 ,w4 ,c41 #aied1 ,geophysical investigations in the emerged and submerged ,atlantic coastal plain4 ,part ,,ix1 ,gulf of ,maine3 ,geol4 ,soc4 ,am4 ,bull41 v4 #ff1 p4 #ieg-igj ,,elmendorf1 ,c4 ,h41 ,,and ,,heezen1 ,b4 ,c41 #aieg1 ,oceanographic information for engineering submarine cable systems3 ,bell ,system ,tech4 ,jour41 v4 ,,xxxvi1 p4 #ajdg-ajic ,,emery1 ,k4 ,o41 #aiej1 ,a deep fathogram across the ,north ,atlantic3 ,am4 ,jour4 ,sci41 v4 #bdh1 p4 #ajj-ajf ,,emiliani1 ,c41 ,,and ,,edwards1 ,g41 #aiec1 ,tertiary ocean bottom temperatures3 ,nature1 v4 #aga1 no4 #dcei1 p4 #hhg-hhh ,,ericson1 ,d4 ,b41 #aieb1 ,north ,atlantic deep-sea sediments and submarine canyons3 ,n4 ,y4 ,acad4 ,sci4 ,trans41 ser4 ,,ii1 v4 #ae1 p4 #ej-ec ,,ericson1 ,d4 ,b41 ,,ewing1 ,m41 ,,and ,,heezen1 ,b4 ,c41 #aiea1 ,deep-sea sands and submarine canyons3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fb1 p4 #ifa-ife ---- #aieb1 ,turbidity currents and sediments in the ,north ,atlantic3 ,amer4 ,assoc4 of ,petrol4 ,geol4 ,bull41 v4 #cf1 p4 #dhi-eab ,,ericson1 ,d4 ,b41 ,,ewing1 ,m41 ,,heezen1 ,b4 ,c41 ,,and ,,wollin1 ,g41 #aiee1 ,sediment deposition in the deep ,atlantic1 p4 #bje-bbj in ,poldervaart1 ,arie1 ,editor1 ,crust of the earth3 ,geol4 ,soc4 ,am4 ,spec4 ,paper #fb1 #gfb p4 ,,ericson1 ,d4 ,b41 ,,ewing1 ,m41 ,,wollin1 ,g41 ,,and ,,heezen1 ,b4 ,c41 in press1 ,two-hundred and twenty-one ,atlantic deep-sea cores3 ,geol4 ,soc4 ,am4 ,,ewing1 ,j4 ,i41 ,,and ,,ewing1 ,w4 ,m41 in press1 ,seismic refraction measurements in the ,atlantic ,ocean basins1 ,mediterranean ,sea1 on the ,mid-,atlantic ,ridge and in the ,norwegian ,sea3 ,geol4 ,soc4 ,am4 ,bull4 ,,ewing1 ,j4 ,i41 ,,officer1 ,c4 ,b41 ,,johnson1 ,h4 ,r41 ,,and ,,edwards1 ,r4 ,s41 #aieg1 ,geophysical investigations of the eastern ,caribbean4 ,trinidad ,shelf1 ,tobago ,trough1 ,barbados ,ridge1 ,atlantic ,ocean3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fh1 p4 #hig-iab ,,ewing1 ,m41 ,,and ,,heezen1 ,b4 ,c41 #aiee1 ,puerto ,rico ,trench topographic and geophysical data1 p4 #bee-bfh in ,poldervaart1 ,arie1 ,editor1 ,crust of the earth3 ,geol4 ,soc4 ,am4 ,spec4 ,paper #fb1 #gfb p4 ---- #aief;a1 ,oceanographic research programs of the ,lamont ,geological ,observatory3 ,geog4 ,rev41 v4 ,,xlvi1 p4 #ejh-ece ---- #aief;b1 ,some problems of ,antarctic submarine geology3 ,antarctica in the ,i4 ,g4 ,y41 ,geophys4 ,mon41 no4 #a1 p4 #ge-ha ,,ewing1 ,m41 ,,and ,,worzel1 ,j4 ,l41 #aied1 ,gravity anomalies and structure of the ,west ,indies1 ,part ,i3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fe1 p4 #afe-agd ,,ewing1 ,m41 ,,crary1 ,a4 ,p41 ,,and ,,rutherford1 ,h4 ,m41 #aicg1 ,geophysical investigations in the emerged and submerged ,atlantic ,coastal ,plain1 ,part ,i3 ,geol4 ,soc4 ,am4 ,bull41 v4 #dh1 p4 #gec-hjb ,,ewing1 ,m41 ,,ericson1 ,d4 ,b41 ,,and ,,heezen1 ,b4 ,c41 #aieh1 ,sediments and topography of the ,gulf of ,mexico1 p4 #iie-ajec in ,weeks1 ,l41 ,editor1 ,habitat of ,oil2 ,amer4 ,assoc4 ,petrol4 ,geol41 ,tulsa1 #achdp4 ,,ewing1 ,m41 ,,heezen1 ,b4 ,c41 ,,and ,,hirshman1 ,j41 #aieg1 ,mid-,atlantic ,ridge seismic belt and magnetic anomalies 7,abstract73 ,comm4 ,no4 #aaj bis4 ,assoc4 ,seismol4 ,ass4 ,gen4 ,u4 ,g4 ,g4 ,i41 ,toronto ,,ewing1 ,m41 ,,sutton1 ,g4 ,h41 ,,and ,,officer1 ,c4 ,b4 ,,jr41 #aied1 ,seismic refraction measurements in the ,atlantic ,ocean1 ,part ,,vi3 ,typical deep stations1 ,north ,america ,basin3 ,seismol4 ,soc4 ,am4 ,bull41 v4 #dd1 p4 #ba-ch ,,ewing1 ,m41 ,,woollard1 ,g4 ,p41 ,,vine1 ,a4 ,c41 ,,and ,,worzel1 ,j4 ,l41 #aidf1 ,recent results in submarine geophysics3 ,geol4 ,soc4 ,am4 ,bull41 v4 #eg1 p4 #iji-icd ,,ewing1 ,m41 ,,heezen1 ,b4 ,c41 ,,ericson1 ,d4 ,b41 ,,northrop1 ,j41 ,,and ,,dorman1 ,j41 #aiec1 ,exploration of the ,northwest ,atlantic ,mid-,ocean ,canyon3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fd1 p4 #hfe-hfh ,,fenneman1 ,n4 ,m41 #aich1 ,physiography of ,eastern ,united ,states3 ,mc,graw-,hill1 ,n4 ,y41 #gad p4 ,,fisher1 ,r4 ,l41 #aied1 ,on sounding in trenches3 ,deep ,sea ,research1 v4 #b1 no4 #a1 p4 #dh-eh ,,frassetto1 ,r41 ,,and ,,northrop1 ,j41 #aieg1 ,virgin ,islands bathymetric survey3 ,deep ,sea ,research1 v4 #d1 p4 #ach-adf ,,furon1 ,r41 #aidi1 ,sur les trilobites dragues #dbee m4 de profondeur par le ,talisman 7#ahhc73 ,c4 ,r4 ,acad1 de ,sci41 ,paris1 t4 #bbh1 p4 #aeji-aeaj ,,gaskell1 ,t4 ,f41 ,,and ,,ashton1 ,w41 #aied1 ,h4 ,m4 ,s4 ,,challenger',s world voyage #aiej-eb4 part #b3 ,intl4 ,hydro4 ,rev41 v4 #ca1 p4 #aja-aaa ,,gibson1 ,w4 ,m41 #aieh1 ,gulf of ,alaska trough parallels ,aleutian ,trench3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fi1 p4 #faa-fad ,,grousson1 ,r41 #aieg1 ,bathymetrie de la cote ,atlantique de ,maroc3 ,ministre de la ,dfense ,nationale1 ,paris1 ,bull4 d',information ,c4,o4,e4,c41 ann4 ,,ix1 no4 #h1 p4 #daa-dab ,,gutenberg1 ,b41 ,,and ,,richter1 ,c4 ,f41 #aied1 ,seismicity of the earth3 ,princeton ,univ4 ,press1 ,princeton1 ,n4 ,j41 #caj p4 ,,hamilton1 ,e4 ,l41 #aief1 ,sunken islands of the ,mid-,pacific ,mountains3 ,geol4 ,soc4 ,am4 ,memoir #fd1 #ig p4 ,,heezen1 ,b4 ,c41 #aied1 ,methods of exploring the ocean floor1 p4 #bjj-bje in ,isaacs1 ,j4 ,d41 and ,iselin1 ,c4 ,o',d41 ,editors1 ,oceanographic ,instrumentation3 ,natl4 ,acad4 of ,sci41 ,publ4 #cji ---- #aief1 ,the origin of the submarine canyons3 ,scient4 ,american1 v4 #aie1 p4 #cf-da ---- ,in preparation1 ,some precision sounding profiles by ,u4,s4,s4 ,,glacier and ,u4,s4,s4 ,,wyandot in ,antarctic waters ,,heezen1 ,b4 ,c41 ,,and ,,ewing1 ,m41 #aieb1 ,turbidity currents and submarine slumps1 and the ,grand ,banks earthquake3 ,am4 ,jour4 ,sci41 v4 #bej1 p4 #hdi-hgc ---- #aiee1 ,orleansville earthquake and turbidity currents3 ,amer4 ,assoc4 ,petrol4 ,geol4 ,bull41 v4 #ci1 p4 #beje-bead ---- ,in press1 ,seismicity of the ,mid-,atlantic ,ridge3 ,amer4 ,geophys4 ,union ,trans4 ,,heezen1 ,b4 ,c41 ,,ericson1 ,d4 ,b41 ,,and ,,ewing1 ,m41 #aied1 ,further evidence for a turbidity current following the #aibi ,grand ,banks earthquake3 ,deep ,sea ,research1 v4 #a1 p4 #aic-bjb ,,heezen1 ,b4 ,c41 ,,ewing1 ,m41 ,,ericson1 ,d4 ,b41 #aiea1 ,submarine topography in the ,north ,atlantic3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fb1 p4 #adjg-adji ---- #aied1 ,reconnaissance survey of the abyssal plain south of ,newfoundland3 ,deep ,sea ,research1 v4 #b1 p4 #abb-acc ,,heezen1 ,b4 ,c41 ,,ewing1 ,m41 ,,and ,,menzies1 ,r4 ,j41 #aiee1 ,the influence of submarine turbidity currents on abyssal productivity3 ,oikos1 v4 #f1 p4 #agj-ahb ---- #aieh1 ,submarine turbidity flows3 ,priroda1 ,feb4 #aieh1 p4 #ajj-ajd 7in ,russian7 ,,heezen1 ,b4 ,c41 ,,ewing1 ,m41 ,,and ,,miller1 ,e4 ,t41 #aiec1 ,trans-,atlantic profile of total magnetic intensity and topography1 ,dakar to ,barbados3 ,deep ,sea ,research1 v4 #a1 p4 #be-cc ,,heezen1 ,b4 ,c41 ,,ewing1 ,m41 ,,ericson1 ,d4 ,b41 ,,and ,,bentley1 ,c4 ,r41 in press1 ,the flat-topped ,atlantis1 ,cruiser and ,great ,meteor seamounts3 ,geol4 ,soc4 ,am4 ,bull4 ,,heezen1 ,b4 ,c41 and others1 in preparation1 ,submarine structural benches and drowned beaches of the ,atlantic ,,hess1 ,h4 ,h41 #aied1 ,geological hypotheses and the earth's crust under the ocean3 ,roy4 ,soc4 ,proc41 ,a4 v4 #bbb1 p4 #cda-cdh ---- #aicc1 ,interpretation of geological and geophysical observations1 ,navy ,princeton gravity expedition to ,west ,indies in #aicb3 ,naval ,observatory ,publ4 no4 #ai1 p4 #bg-ed ,,hill1 ,m4 ,n41 #aied1 ,topography of the ,mid-,atlantic ,ridge 7,abstract73 ,abstracts of ,rome meeting of ,u4,g4,g4,i4 ---- #aief1 ,notes on the bathymetric chart of the northeast ,atlantic3 ,deep ,sea ,research1 v4 #c1 p4 #bbi-bca ---- #aieg1 ,recent geophysical exploration of the ocean floor1 p4 #abi-afc in ,ahrens1 ,l4 ,h41 et al41 ,editors1 ,physics and chemistry of the earth3 ,pergamon ,press1 ,london1 #bei p4 ,,johnson1 ,,douglas1 #aici1 ,origin of submarine canyons3 ,columbia ,univ4 ,press1 ,new ,york1 #baf p4 ,,katz1 ,s41 ,,and ,,ewing1 ,m41 #aiee1 ,seismic-refraction measurements in the ,atlantic ,ocean1 ,part ,,vii1 ,atlantic ,ocean basin west of ,bermuda3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fg1 p4 #dge-eaj ,,kay1 ,m41 #aiea1 ,north ,american geosynclines3 ,geol4 ,soc4 ,am4 ,memoir #dh1 #adc p4 ,,keller1 ,f4 ,j41 ,,meuschke1 ,j4 ,l41 ,,and ,,alldredge1 ,l4 ,r41 #aied1 ,aeromagnetic surveys in the ,aleutian1 ,marshall1 and ,bermuda islands3 ,amer4 ,geophys4 ,union ,trans41 v4 #ce1 p4 #eeh-egb ,,knott1 ,s4 ,t41 ,,and ,,hersey1 ,j4 ,b41 #aief1 ,interpretation of high resolution echo-sounding techniques and their use in bathymetry1 marine geophysics1 and geology3 ,deep ,sea ,research1 v4 #d1 p4 #cf-dd ,,koczy1 ,f4 ,f41 #aied1 ,a survey on deep sea features taken during the ,swedish ,deep ,sea ,expedition3 ,deep ,sea ,research1 v4 #a1 p4 #agj-ahd ---- #aief1 ,echo soundings1 ,reports of ,swedish ,deep ,sea ,expeditions1 v4 ,,iv1 ,bottom investigations3 ,fasc4 ,,ii1 p4 #ii-aeh1 ,gteborgs ,kungl4 ,vetenskaps-och vitterhetssamhlle ,,kuenen1 ,,ph4 ,h41 #aiej1 ,marine geology3 ,wiley1 ,new ,york1 #efh p4 ,,lee1 ,c4 ,s41 #aiea1 ,geophysical surveys on the ,bahama ,banks3 ,inst4 ,petrol4 ,jour4 ,london1 v4 #cg1 no4 #ccd1 p4 #fcc-feg ,,lobeck1 ,a4 ,k41 #aibd1 ,block diagrams3 ,wiley1 ,new ,york1 #bjf p4 ---- #aici1 ,geomorphology3 ,mc,graw-,hill1 ,new ,york1 #gca p4 ---- #aidh1 ,physiographic diagram of the ,united ,states3 ,geog4 ,press1 ,n4 ,y4 ,,luskin1 ,b41 ,,and ,,israel1 ,h4 ,g41 #aief1 ,precision depth recorder ,,mk-,v3 ,lamont ,geological ,observatory and ,time ,facsimile ,corp41 ,tech4 ,rept4 no4 #ab1 #ca p4 ,,luskin1 ,b41 ,,heezen1 ,b4 ,c41 ,,ewing1 ,m41 ,,and ,,landisman1 ,m41 #aied1 ,precision measurements of ocean depth3 ,deep ,sea ,research1 v4 #a1 p4 #aca-adj ,,matthews1 ,d4 ,j41 #aici1 ,tables of the velocity of sound in pure water and sea water for use in echo sounding and echo ranging3 ,admiralty ,hydrographic ,dept41 ,london1 #eb p4 ,,maury1 ,m4 ,f41 #ahee1 ,physical geography of the sea3 ,harpers1 ,new ,york1 #chi p4 ,,menard1 ,h4 ,w41 #aiee1 ,deep sea channels1 topography and sedimentation1 ,amer4 ,assoc4 ,petrol4 ,geol4 ,bull41 v4 #ci1 p4 #bcf-bee ,,miller1 ,e4 ,t41 ,,and ,,ewing1 ,m41 #aief1 ,geomagnetic measurements in the ,gulf of ,mexico and in the vicinity of ,caryn ,peak3 ,geophysics1 v4 ,,xxi1 p4 #djf-dcb ,,murray1 ,h4 ,w41 #aidg1 ,topography of the ,gulf of ,maine3 ,geol4 ,soc4 ,am4 ,bull41 v4 #eh1 p4 #aec-aif ,,murray1 ,j41 ,,and ,,hjort1 ,j41 #aiab1 ,depths of the ocean3 ,john ,murray1 ,london1 #hba p4 ,,nafe1 ,j41 ,,and ,,drake1 ,c4 ,l41 #aieg1 ,variation with depth in shallow and deep water marine sediments of porosity1 density and the velocities of compressional and shear waves3 ,geophysics1 v4 ,,xxii1 p4 #ebc-eeb ,,newell1 ,n4 ,d41 #aiee1 ,bahamian platforms1 p4 #cjc-caf in ,poldervaart4 ,arie1 ,editor1 ,crust of the earth3 ,geol4 ,soc4 ,am4 ,special ,paper #fb1 #gfb p4 ,,northrop1 ,j41 ,,and ,,frosch1 ,r41 #aied1 ,seamounts in the ,north ,america basin3 ,deep ,sea ,research1 v4 #a1 p4 #beb-beg ,,northrop1 ,j41 ,,and ,,heezen1 ,b4 ,c41 #aiea1 ,an outcrop of ,eocene sediment on the continental slope3 ,jour4 ,geol41 v4 #ei1 p4 #cfi-cii ,,officer1 ,c4 ,b41 ,,and ,,ewing1 ,m41 #aied1 ,geophysical investigations in the emerged and submerged ,atlantic coastal plain1 ,part ,,vii1 ,continental shelf1 continental slope1 and continental rise south of ,nova ,scotia3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fe1 p4 #fec-fgj ,,officer1 ,c4 ,b41 ,,ewing1 ,m41 ,,and ,,wuenschel1 ,p4 ,c41 #aieb1 ,seismic refraction measurements in the ,atlantic ,ocean basin1 ,part ,,iv1 ,bermuda1 ,bermuda ,rise1 and ,nares ,basin3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fc1 p4 #ggg-hji ,,officer1 ,c4 ,b41 ,,ewing1 ,j4 ,i41 ,,edwards1 ,r4 ,s41 ,,and ,,johnson1 ,h4 ,r41 #aieg1 ,geophysical investigations in the eastern ,caribbean4 ,venezuelan ,basin1 ,antilles ,island ,arc1 and ,puerto ,rico ,trench3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fh1 p4 #cei-cgh ,,pettijohn1 ,f4 ,j41 #aieg1 ,sedimentary rocks3 ,harpers1 ,new ,york1 #gah p4 ,,press1 ,f41 ,,and ,,beckmann1 ,w4 ,c41 #aied1 ,geophysical investigations in the emerged and submerged ,atlantic coastal plain1 ,part ,,viii1 ,grand ,banks and adjacent shelves3 ,geol4 ,soc4 ,america ,bull41 v4 #fe1 p4 #bii-cad ,,raisz1 ,e41 #aieb1 ,landforms of the ,united ,states3 ,harvard ,univ41 ,cambridge1 ,mass4 ,,raitt1 ,r4 ,w41 #aief1 ,seismic-refraction studies of the ,pacific ,ocean basin1 ,part ,i1 ,crustal thickness of the equatorial ,pacific3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fg1 p4 #afbc-afdj ,,richards1 ,h4 ,j41 ,,and ,,ruhle1 ,j4 ,l41 #aiee1 ,mollusks from a sediment core from the ,hudson submarine canyon3 ,pa4 ,acad4 ,sci4 ,proc41 v4 ,,xxix1 p4 #ahf-aij ,,schott1 ,g41 #aidb1 ,geographie des ,atlantischen ,ozeans3 ,c4 ,boysen1 ,hamburg1 #dch p4 ,,sch,,ler1 ,f41 #aieb1 ,on the accuracy of configuration of sea bottom profiles with high frequency echo sounders3 ,intl4 ,hydro4 ,review1 v4 ,,vii1 p4 #abf-ace ,,shand1 ,s4 ,j41 #aidi1 ,rocks of the ,mid-,atlantic ,ridge3 ,jour4 ,geol41 v4 #eg1 p4 #hi-ib ,,shepard1 ,f4 ,p41 #aica1 ,saint ,lawrence 7,cabot ,strait7 submarine trough3 ,geol4 ,soc4 ,am4 ,bull41 v4 #db1 p4 #hec-hfd ---- #aidh1 ,submarine geology3 ,harpers1 ,new ,york1 #cdh p4 ,,shepard1 ,f4 ,p41 ,,and ,,cohee1 ,g4 ,v41 #aicf1 ,continental shelf sediments off the ,mid-,atlantic states1 ,geol4 ,soc4 ,am4 ,bull41 v4 #dg1 p4 #dda-deg ,,shepard1 ,f4 ,p41 ,,treffenden1 ,j4 ,m41 ,,and ,,cohee1 ,g4 ,v41 #aicd1 ,origin of ,georges ,bank3 ,geol4 ,soc4 ,am4 ,bull41 v4 #de1 p4 #bha-cjb ,,shurbet1 ,g4 ,l41 ,,and ,,worzel1 ,j4 ,l41 #aieg1 ,gravity anomalies and structure of the ,west ,indies1 ,part ,,iii3 ,geol4 ,soc4 ,am4 ,bull41 v4 #fh1 p4 #bfc-bff ,,smith1 ,e4 ,h41 ,,soule1 ,f4 ,m41 ,,and ,,mosby1 ,o41 #aicg1 ,,marion and ,,general ,,greene expeditions to ,davis ,strait and ,labrador ,sea under the direction of the ,u4 ,s4 ,coast ,guard1 #aibh-aica-aicc-aicd-aice3 ,u4 ,s4 ,coast ,guard ,bull41 v4 #ai1 p4 #a-bei ,,smith1 ,w4 ,o41 ,,upson1 ,j4 ,e41 and others1 #aieb1 ,preliminary report on the ,passamaquoddy bedrock survey1 ,july-,august #aiea3 ,u4 ,s4 ,geol4 ,survey ,water ,resources ,division1 #di p4 ,,spangler1 ,w4 ,b41 #aiej1 ,subsurface geology of ,atlantic coastal plain of ,north ,carolina3 ,amer4 ,assoc4 ,petrol4 ,geol4 ,bull41 v4 #cd1 p4 #ajj-acb ,,spangler1 ,w4 ,b41 ,,and ,,peterson1 ,j4 ,j41 #aiej1 ,geology of ,atlantic coastal plain in ,new ,jersey1 ,delaware1 ,maryland1 and ,virginia3 ,amer4 ,assoc4 ,petrol4 ,geol4 ,bull41 v4 #cd1 p4 #a-ii 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,,and ,,smith1 ,p4 ,a41 #aici1 ,atlantic submarine valleys of the ,united ,states and the ,congo ,submarine ,valley3 ,geol4 ,soc4 ,am4 ,special ,paper #g1 #aja p4 ,,washington1 ,h4 ,s41 #aicj1 ,origin of the ,mid-,atlantic ,ridge3 ,md4 ,acad4 ,sci4 ,jour41 v4 #a1 p4 #bj-bi ,,wiseman1 ,j4 ,h4 ,d41 ,,and ,,ovey1 ,c4 ,d41 #aiej1 ,recent investigations on the deep sea floor3 ,geol4 ,assoc4 ,proc41 v4 #fa1 p4 #bh-hd ---- #aiec1 ,definitions of features on the deep sea floor3 ,deep ,sea ,research1 v4 #a1 p4 #aa-af ---- #aiee1 ,proposed names of features on the deep sea floor #b2 ,general principles governing the allocation of names3 ,deep ,sea ,research1 v4 #b41 p4 #bfa-bfc ,,worzel1 ,j4 ,l41 ,,and ,,shurbet1 ,g4 ,l41 #aiee;a1 ,gravity interpretations from crustal sections1 p4 #hg-ajj in ,poldervaart1 ,arie1 ,editor1 ,crust of the earth1 ,geol4 ,soc4 ,am4 ,special ,paper #fb1 #gfb p4 ---- #aiee;b1 ,the ,toro ,seamount3 ,geol4 ,soc4 ,am4 ,bull41 v4 #ff1 p4 #dfe-dff ,,worzel1 ,j4 ,l41 ,,and 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,erg41 ,bd4 ,,vi1 ,teil #b1 #dbj p4 ,,zeigler1 ,j41 ,,athearn1 ,w4 ,d41 ,,and ,,small1 ,h41 #aieg1 ,profiles across the ,peru-,chile trench3 ,deep ,sea ,research1 v4 #d1 p4 #bch-bdi ,,author ,,index ,agostinho1 ,j41 #ih1 #aji ,alldredge1 ,l4 ,r41 #ea1 #aaa ,andrade1 ,c4 ,f4 de1 #e1 #ba1 #cg1 #aji ,armstrong1 ,j4 ,c41 #cf1 #aji ,ashton1 ,w41 #ee1 #aaj ,athearn1 ,w4 ,d41 #fj1 #aac ,atwood1 ,w4 ,w41 #aa1 #aji ,bartholomew1 ,j4 ,c41 #e1 #aji ,beckmann1 ,w4 ,c41 viii1 #bc1 #ff1 #aji1 #aab ,behm1 ,a41 #h ,bentley1 ,c41 #ih1 #aji1 #aaa ,berckhemer1 ,h41 #gi1 #aab ,bourcart1 ,j41 #cg1 #di1 #aji ,bucher1 ,w4 ,h41 viii ,bullard1 ,e4 ,c41 #di1 #eb1 #ajc1 #aji ,cloos1 ,h41 #ih1 #aji ,cohee1 ,g4 ,v41 #ec1 #aab ,crary1 ,a4 ,p41 #dc1 #aaj ,dahl1 ,w4 ,h41 #dc1 #aji ,davidson1 ,m4 ,j41 viii1 #eb1 #aji ,day1 ,a4 ,a41 #di1 #aji ,deacon1 ,g4 ,e4 ,r41 viii de ,smitt1 ,v4 ,p41 #fg1 #aji ,dietrich1 ,g41 #e1 #aji ,dietz1 ,r4 ,s41 #h1 #ff1 #aji ,dorman1 ,j41 #ff1 #gj1 #gd1 #aaj ,drake1 ,c4 ,l41 vii1 #ej1 #eb1 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,volcanoes1 #ci1 #gg1 #gh ,west ,europe ,basin1 #ab ,west ,florida ,escarpment1 #cc ,woods ,hole ,oceanographic ,institution1 vii1 viii1 #c1 #g ,yorktown 7,miocene7 formation1 #dd1 #de1 #df ,illustration3 ,heezen et al41 ,,pl4 #bj ,,physiographic ,,provinces1 ,,atlantic ,,ocean_/a ,illustration3 ,heezen et al41 ,,pl4 #ba ,,control ,,chart ,all continuously recorded echo-sounding profiles used in preparation of ,plates #a and #bj are shown4 ,solid lines indicate ,lamont ,geological ,observatory and ,woods ,hole ,oceanographic ,institution cruises4 ,dashed lines indicate soundings supplied by ,british ,admiralty4 ,lines shown by alternate long dash and two short dashes indicate closely spaced discrete soundings of ,,meteor4 ,illustration3 ,heezen et al41 ,,pl4 #bb ,,six ,,trans-,,atlantic ,,topographic ,,profiles ,soundings in fathoms continuously recorded by an ,,nmc echo sounder on the ,r4 ,v4 ,,atlantis4 ,the letters amdash2q indicate where soundings from different cruises were joined4 ,illustration3 ,heezen et al41 ,,pl4 #bc ,,index ,,chart ,,showing ,,locations ,,of ,,profiles ,,of ,,plates #bd1 #be1 #bf ,,and ,,figure #de ,illustration3 ,heezen et al41 ,,pl4 #bd ,,thirty-,,four ,,profiles ,,of ,,the ,,continental ,,margin3 ,,western ,,north ,,atlantic ,profile locations shown on ,plate #bc4 ,note small topographic details4 ,soundings spaced approximately #a mile apart4 ,illustration3 ,heezen et al41 ,,pl4 #be ,,twenty-,,three ,,profiles ,,of ,,the ,,continental ,,margin ,,of ,,europe ,,and ,,africa ,illustration3 ,heezen et al41 ,,pl4 #bf ,,crustal ,,structure ,,and ,,continental-,,margin ,,provinces ,,four ,,representative ,,profiles1 ,,positions ,,of ,,profiles ,,shown ,,on ,,plate #bc4 ,data for ,w-#f from ,bentley and ,worzel 7#aief71 ,w-#aj and ,w-#aa from ,katz and ,ewing 7#aiee71 and ,w-#cc from ,ewing and ,worzel 7#aied7 and ,officer et al4 7#aieg74 ,seismic data projected to continuously recorded sounding profiles4 ,vertical exaggeration #dj3a4 ,illustration3 ,heezen et al41 ,,pl4 #bg ,,five ,,topographic ,,profiles1 ,,western ,,north ,,atlantic ,soundings continuously recorded on ,,nmc sounder4 ,illustration3 ,heezen et al41 ,,pl4 #bh ,,distribution ,,of ,,deep-,,sea ,,sands ,,in ,,relation ,,to ,,physiographic ,,provinces ,data from ,ericson et al4 7#aieb2 #aiee7 based on piston cores taken by ,lamont ,geological ,observatory expeditions4 ,illustration3 ,heezen et al41 ,,pl4 #bi ,,earthquake ,,epicenters1 ,,north ,,atlantic ,date from ,gutenberg and ,richter 7#aied7 and the epicenter cards of the ,u4,s4 ,coast and ,geodetic ,survey through #aief4 ,illustration3 ,heezen et al41 ,,pl4 #cj ,,location ,,of ,,pdr ,,records ,,and ,,bottom ,,photographs ,,reproduced ,,as ,,illustrations4 ,transcriber's ,notes3 ,the large diagram for plate #a mentioned in the note on p4 v is missing4 ,it was not physically attached to the book per note4 ,silently corrected simple spelling1 grammar1 and typographical errors4 ,retained anachronistic and non-standard spellings as printed4 ,enclosed italics markup in underscores4