,,the ,,earth ,,seen ,,from ,,the ,,air ,illustration3 ,,fig4 #a--,the ,national ,capitol1 ,washington1 ,d4 ,c4 ,a view obliquely downward from a position over the ,national ,botanical ,garden1 showing the western front of the ,capitol at the approach to it from ,pennsylvania ,avenue4 ,in the background1 at the right1 can be seen a part of the ,library of ,congress and1 at the left1 a part of the ,senate ,office ,building4 ,the radiating avenues of approach are of interest as well as the character of the district surrounding the ,capitol1 as indicated by the apartment houses and tree-lined streets4 ,,american ,,geographical ,,society ,,special ,,publication ,,no4 #d ,w4 ,l4 ,g4 ,,joerg1 ,editor ,,the ,,face ,,of ,,the ,,earth ,,as ,,seen ,,from ,,the ,,air ,a ,study in the ,application of ,airplane ,photography to ,geography ,,by ,,willis ,t4 ,,lee ,u4 ,s4 ,geological ,survey ,illustration ,,american ,,geographical ,,society ,,broadway ,,at #aef,,th ,,street ,,new ,,york #aibb ,,copyright1 #aibb ,,by ,,the ,,american ,,geographical ,,society ,,of ,,new ,,york ,,cond ,,nast ,,press ,,greenwich1 ,,conn4 ,,contents ,,chapter ,,page ,,introduction ix ,i ,,the ,,viewpoint #a ,,ii ,,familiar ,,scenes ,,from ,a ,,new ,,angle #g ,,iii ,,architecture1 ,,landscape ,,gardening1 ,,and ,,engineering #aa ,,iv ,,the ,,mosaic #bj ,v ,,general ,,aspects ,,of ,,the ,,surface ,,as ,,seen ,,from ,,the ,,air #bb ,,vi ,,marshes ,,and ,,marsh ,,drainage #bg ,,vii ,,coastal ,,mud ,,flats #da ,,viii ,,submerged ,,land ,,forms #de ,,ix ,,the ,,plain ,,from ,,the ,,air #ej ,x ,,mountain ,,features #eg ,,xi ,,air ,,craft ,,in ,,the ,,study ,,of ,,rocks ,,and ,,ores #fi ,,xii ,,mapping ,,and ,,charting ,,from ,,the ,,air #gb ,,index #aje ,,list ,,of ,,illustrations 7o7 indicates an oblique1 7v7 a vertical airplane photograph ,,fig4 ,,page ,,the ,,viewpoint1 ,,and ,,familiar ,,scenes ,,from ,a ,,new ,,angle #a ,the ,national ,capitol1 ,washington1 ,d4 ,c4 7o7 ,frontispiece #b ,symbols of automatic register in the ,eastman mapping camera 7v7 #c #c ,the ,united ,states ,military ,academy1 ,west ,point1 ,n4 ,y4 7o7 #h #d ,the ,united ,states ,naval ,academy1 ,annapolis1 ,md4 7o7 #i ,,architecture1 ,,landscape ,,gardening1 ,,and ,,engineering #e ,monument ,avenue1 ,richmond1 ,va4 7o7 #ab #f ,the ,united ,states ,naval ,observatory1 ,washington1 ,d4 ,c4 7o74 #ac #g ,shipyards at ,newport ,news1 ,va4 7o7 #ad #h ,the ,new ,york ,connecting ,railroad ,bridge 7o7 #ae #i ,a part of ,washington1 ,d4 ,c4 7o7 #af #aj ,part of ,rockaway ,beach1 ,long ,island1 ,n4 ,y4 7v7 #ag #aa ,part of ,long ,branch1 ,n4 ,j4 7v7 #ah #ab ,benning1 ,d4 ,c41 and the ,anacostia ,river 7v7 #bb #ac ,the land along the ,anacostia ,river on the eastern edge of ,washington1 ,d4 ,c4 7v7 facing #bb #ad ,map of the same area as in ,fig4 #ac facing #bb ,,general ,,aspects ,,of ,,the ,,surface #ae ,southeastern part of ,mulberry ,island on the lower ,james ,river1 ,maryland 7v7 #bd #af ,map of the same area as in ,fig4 #ae #be #ag ,columbus1 ,ga4 7v7 facing #bf #ah ,map of the same area as in ,fig4 #ag facing #bf ,,marshes ,,and ,,coastal ,,mud ,,flats #ai ,tidal marsh and ocean beach at ,corsons ,inlet1 ,new ,jersey 7v7 #bh #bj ,details of marshland1 ,lee ,marsh1 lower ,pamunkey ,river1 ,virginia 7v7 #cj #ba ,details of marshland1 ,cousaic ,marsh1 lower ,pamunkey ,river1 ,virginia 7v7 #ca #bb ,barrier beach from ,corsons ,inlet to ,atlantic ,city1 ,n4 ,j4 7v7 #cb #bc ,a river system in miniature near ,hampton1 ,virginia 7v7 #cc #bd ,sweet ,hall ,marsh on the lower ,pamunkey ,river1 ,virginia 7v7 #cd #be ,map of the same area as in ,fig4 #bd1 with cross section #ce #bf ,eltham ,marsh on the lower ,pamunkey ,river1 ,virginia 7v7 #cf #bg ,map of the same area as in ,fig4 #bf1 with cross section #cg #bh ,a stream system of the mud-flat area off the ,eastern ,shore of ,virginia 7v7 #db #bi ,mud-flat streams 7v7 #dc ,,submerged ,,land ,,forms #cj ,stove ,point ,neck at the mouth of the ,piankatank ,river1 ,virginia 7v7 #df #ca ,gwynn ,island at the mouth of the ,piankatank ,river1 ,virginia 7v7 #df #cb ,map showing the location of ,figs4 #ca and #cb1 with cross section #dg #cc ,a drowned valley3 ,lambs ,creek1 ,chesapeake ,bay1 ,virginia 7v7 #dh ,,the ,,plain ,,from ,,the ,,air #cd ,the ,chattahoochee ,river south of ,columbus1 ,ga4 7v7 facing #ej #ce ,map of the same area as in ,fig4 #cd facing #ej #cf ,a river channel in the ,great ,plains3 ,the ,red ,river northeast of ,wichita ,falls1 ,tex4 7v7 #ea #cg ,a glacial drift plain in southwestern ,michigan 7v7 #eb #ch ,map of the same area as in ,fig4 #cg #ec #ci ,schoolcraft1 ,mich4 7v7 #ed #dj ,map of the same area as in ,fig4 #ci #ee #da ,kettleholes in glacial till southwest of ,schoolcraft1 ,mich4 7v7 #ef ,,mountain ,,features #db ,mt4 ,shasta1 ,california 7o7 #eh #dc ,a glacial gorge on the northeastern face of ,mt4 ,shasta 7o7 #ei #dd ,yosemite ,valley1 ,california 7o7 #fj #de ,map showing the angle of vision of ,fig4 #dd #fa #df ,cinder ,cone on the eastern edge of the northern ,sierra ,nevada1 ,california 7o7 #fb #dg ,map showing the angle of vision of ,fig4 #df #fc #dh ,the top of ,cinder ,cone 7o7 #fd #di ,simi ,hills northwest of ,santa ,monica1 ,cal4 7v7 #fe #ej ,part of ,santa ,monica ,mountains north of ,santa ,monica1 ,cal4 7v7 #ff #ea ,map of the region between the center of ,los ,angeles and ,santa ,monica1 ,cal41 showing the location of ,fig4 #ej #fg #eb ,a young mountain gorge in the ,san ,joaquin ,hills1 a coastal range in ,southern ,california 7v7 #fh #ec ,canyon in sedimentary rocks near the mouth of the ,pecos ,river1 ,texas 7v7 #gj ,,mapping ,,and ,,charting ,,from ,,the ,,air #ed ,view across the western end of ,lake ,erie 7o7 #gc #ee ,map showing the angle of vision of ,fig4 #ed #gc #ef ,rochester1 ,n4 ,y4 7v7 facing #gd #eg ,map of the same area as in ,fig4 #ef facing #gd #eh ,index map showing the location of the airplane photographs in this book taken on the ,atlantic seaboard of the northeastern ,united ,states #ge #ei ,marshlands on ,chesapeake ,bay south of the mouth of the ,york ,river1 ,virginia 7v7 #gf #fj ,left shore of the ,york ,river northwest of ,gloucester ,point1 ,va4 7v7 #gg #fa ,the northwestern tip of ,sandy ,hook1 ,new ,jersey 7v7 #gh #fb ,beach cusps under water near ,beach ,haven1 ,n4 ,j4 7v7 #hj #fc ,first stage in the formation of an inlet through a barrier beach3 near ,beach ,haven1 ,n4 ,j4 7v7 #ha #fd ,a tidal delta in ,shark ,river ,inlet1 ,belmar1 ,n4 ,j4 7v7 #hb #fe ,a tidal delta1 ,popes ,creek on the lower ,potomac ,river1 ,virginia 7o7 #hc #ff ,a double tidal delta at ,barnegat ,inlet1 ,new ,jersey 7v7 #hd #fg ,a tidal inlet through the barrier beach south of ,beach ,haven1 ,n4 ,j4 7v7 #he #fh ,beach between ,brigantine and ,little ,egg ,inlets1 ,new ,jersey 7v7 #hf #fi ,a simple spit3 ,lower ,cedar ,point1 ,maryland1 on the lower ,potomac ,river 7o7 #hg #gj ,a recurved spit south of ,brigantine ,inlet1 ,new ,jersey 7v7 #hh #ga ,a recurved spit showing interference with natural growth3 ,the northern end of ,ocean ,city1 ,n4 ,j4 7v7 #hi #gb ,new ,point ,comfort at the tip of the ,york-,rappahannock peninsula1 ,virginia 7v7 #ij #gc ,spit at ,tucker ,beach1 ,new ,jersey 7v7 #ia #gd ,a land-tied island3 ,napatree ,point1 near ,watch ,hill1 ,r4 ,i4 7v7 #ib #ge ,powells ,creek1 ,virginia1 on the lower ,potomac ,river 7o7 #ic #gf ,roberts ,creek1 a drowned river valley southeast of ,yorktown1 ,va4 7v7 #id #gg ,the underwater channel in ,quantico ,bay on the lower ,potomac ,river1 ,virginia 7v7 #ie #gh ,natural channels and shoals near ,miami4 ,fla4 7o7 #if #gi ,a dredged channel at ,miami1 ,fla4 7o7 #ig #hj ,a shoal in ,hereford ,inlet north of ,wildwood1 ,n4 ,j4 7v7 #ih #ha ,sand bars at ,cape ,charles1 ,va4 7v7 #ii #hb ,bars1 channels1 beaches1 and marsh near ,far ,rockaway1 ,long ,island1 ,n4 ,y4 7v7 #ajj ,all of the airplane photographs in this book1 both oblique and vertical1 were taken by the ,united ,states ,army ,air ,service1 except ,figs4 #gh and #gi1 which were taken by the ,united ,states ,navy ,air ,service1 and ,figs4 #aj1 #fe1 #fi1 #ge1 #gg1 and #hb1 which were taken by the author4 ,to these two services the author is indebted for the permission to reproduce their photographs1 and this acknowledgment is made with the same force as if made individually under each illustration4 ,as a guide to the evaluation of the scale of the vertical photographs1 which is expressed under each photograph in the form of the natural scale1 or representative fraction1 the following approximate equivalents may be borne in mind3 #a3aj1jjj #hjj feet to the inch #a3af1jjj mile to the inch #a3ba1jjj mile to the inch ,,introduction ,scarcely a generation has passed during the evolution of the airplane from a ridiculous dream to a practical factor in the work of the world4 ,men who once read with derision1 or only passive interest at best1 of the experiments of ,langley1 ,chanute1 and the ,wrights have seen the airplane developed suddenly into an indispensable instrument of war and an agency of demonstrated value and of such diversity of application that its future is hard to estimate4 ,the navigation of the air has accomplished much in many fields4 ,not only does it offer a new means of efficiency in military reconnaissance1 rapid delivery of mail1 fire patrol of forests1 and the constantly increasing number of commercial and scientific pursuits to which it is being adapted2 but it has also opened a new world to the geographer1 the physiographer1 and the geologist4 ,,airplane ,,photography3 ,,its ,,development ,,and ,,application ,very early in the war the airplane was recognized as a useful1 in fact a necessary1 means of observing enemy positions and movements4 ,but the speed of the airplane was found to preclude the taking of more than the most hurried of notes during a flight1 and notes written from memory are not the most satisfactory4 ,photography was found to obviate this difficulty4 ,the ability of the camera to make instantaneous exposures and fix a clear image on a photographic plate enabled the observer to obtain a record not only of the scenes that he had viewed but also of many that he might have missed while engaged in the necessary business of watching the sky for the enemy--a record that for detail and accuracy could not be approached by the most elaborate notes or the most graphic description4 ,immediately inventive genius was set at work to adjust the mechanism of the camera to the demands of air photography and to prepare the rapidly working films and highly sensitized paper necessary for the best results4 ,so satisfactory were the results and so great are the possibilities of further adaptation that there is an unfortunate tendency on the part of certain enthusiasts to make exaggerated claims that may react to retard progress4 ,this is particularly true in the use of the air photograph in mapping4 ,there are limitations to this use of air photography4 ,it cannot be reasonably expected to do away entirely with the ground work of the surveyor4 ,rather1 the camera is to be regarded as one of the instruments of the surveyor4 ,observation from the air can never take the place of close examination of the ground1 but it can be of great use in the location and study of land forms and geologic relations4 ,air photography is only an added means of obtaining information1 although it promises to become a very important means4 ,observations from the air described in numerous reports and articles in geographic magazines during the war and since its close indicate that air craft1 especially in connection with air photography1 can be of great use in studying the physical features of the face of the earth4 ,in order to make a practical test of the use of the airplane in the study of geography the writer spent about nine months during the year #aibj making flights1 taking pictures from air craft1 and gathering information from various sources4 ,this book embodies the chief results4 ,the material presented here is by way of illustrating the possibility of using the airplane and airplane photography as a means of securing information that should become increasingly useful in the study of geography1 and of showing geographic and geologic features better than in any other way4 ,the views have been chosen to illustrate the three uses of air photographs with which this book deals--the presentation of new views of subjects of popular interest and the practical value of such views2 the study of land forms from a new and advantageous point of view2 and the use of the air photograph as an aid in mapping4 ,in presenting these illustrations there is no intention that the list of types should be considered in any sense complete4 ,physiographic observation from the air is a relatively new undertaking1 and results are limited and imperfect4 ,as improvements in mechanism and technique are made1 observations will be extended and better photographs and a greater variety of them will be secured4 ,such as are presented here1 however1 serve to demonstrate that the air photograph will come to be recognized as a valuable source of information for the student of geography and geology4 ,,acknowledgments ,the results here presented were secured by the co-operation of the ,air ,services of the ,united ,states ,army and ,navy4 ,hydroplanes were placed at my disposal on several occasions1 and a number of flights were made over water bodies1 particularly over the ,potomac ,river1 ,chesapeake ,bay1 and ,new ,york ,harbor4 ,but the information was gathered chiefly through the ,army ,air ,service4 ,many flights were made in army planes1 some for general observation1 others for photographing specific objects4 ,also the army photographers1 particularly those at ,langley ,field1 near ,newport ,news1 ,va41 made several photographic trips at my request1 and a large number of prints were furnished from negatives stored at this and other flying fields4 ,in this connection ,i wish to express appreciation for the many courtesies extended by ,major ,general ,c4 ,t4 ,menoher1 ,u4 ,s4 ,a41 ,chief of ,air ,service at the time the work was done1 and by ,major ,j4,w4 ,simons1 ,jr41 ,a4,s41 ,acting ,administrative ,executive1 ,air ,service4 ,these officers placed at my disposal every facility of the service that ,i could use4 ,it would be a pleasure1 if space allowed1 to mention the names of the numerous pilots and other officers to whom ,i am directly indebted for the safe completion of some of the most thrilling adventures of my life4 ,i must1 however1 mention the officer to whom ,i am perhaps more indebted than to any other4 ,my introduction to this study was through ,major ,j4,w4 ,bagley of the ,united ,states ,army ,engineering ,corps1 who has done much toward making the camera a valuable instrument in mapping4#a ,through his active interest ,i became acquainted with the officials of the ,army ,air ,service1 who gave the necessary authorization for flights and for securing most of the photographs used to illustrate this book4 ,during the time spent at this work ,i retained my position as geologist of the ,united ,states ,geological ,survey4 ,hence the work is one of co-operation chiefly between the ,united ,states ,army ,air ,service and the ,united ,states ,geological ,survey1 and to a lesser degree with the ,united ,states ,navy ,air ,service4 ,,chapter ,i ,,the ,,viewpoint 7,,figs4 #a ,,to #d7 ,,oblique ,,and ,,vertical ,,airplane ,,photographs ,air photographs are1 in general1 of two sorts1 depending upon whether the photograph was taken with the camera pointing vertically or obliquely downward4 ,in either case the air photographer is free from the limitations that hamper the ground photographer in choosing a point of view4 ,for he can ascend to any desired height and not only select an advantageous position from which to photograph the feature which he wishes to emphasize but also1 at the same time1 avoid obstacles which might obstruct his view from the ground4 ,vertical photographs are preferable where the accurate location of objects is desired4 ,when properly taken they serve many of the purposes of maps and are1 in many ways1 even more useful than maps4 ,they furnish the untrained mind with much of the information that the trained mind reads from a topographic map and1 in addition1 supply details and relations that a map cannot depict4 ,exact accuracy1 however1 cannot be claimed for them until they have been corrected for distortion and adjusted to some system of controls4 ,where the photograph is to be used as a means of securing a more advantageous view of a subject than can be had from the ground rather than as a map on which distances are to be scaled off1 the oblique photograph is probably the more desirable1 since it is as easily intelligible as a photograph taken laterally4 ,the advantage of such photographs is obvious4 ,to the architect1 the landscape gardener1 the city planner is given the opportunity to study their projects free from all obstructions yet in such perspective that their relations to their surroundings are brought out as would be possible by no other means4 ,views like that of ,west ,point 7,fig4 #c7 are occasionally to be had from some hilltop1 but the limited choice of position on the ground contrasts sharply with the unlimited choice in the air4 ,,elements ,,to ,,be ,,recorded ,air photography is by no means simple4 ,much still remains to be done by way of adapting the camera to its peculiar demands4 ,its present degree of perfection1 of course1 is largely due to the impetus given its development during the war because of its great importance in military reconnaissance4 ,the adaptation of the camera to operation from the airplane might be described with profit but will be passed with slight mention because it is the results of air photography rather than the mechanism that are to be considered here4 ,technically1 a photograph of the earth's surface may not be a map1 but1 given certain means of interpretation1 it can be made to serve as such4 ,in using air photographs1 particularly the vertical ones1 it is desirable to know the scale1 which is dependent upon the altitude at which the exposure is made2 the angle of the lens2 and the variation from the vertical1 in order to make corrections for distortion4 ,therefore1 it is desirable that each photograph show the altitude1 date1 time of day1 and position of the lens at which the exposure was made4 ,cameras have been constructed that automatically record these data on each negative4 ,this information is illustrated in ,figure #b4 ,the circular symbol at the left in the white strip at the top of the photograph represents a circular level1 or inclinometer4 ,the small round dot close to the center of the inclinometer indicates that1 at the time the exposure was made1 the axis of the lens was very nearly vertical4 ,the symbol in the center of the white strip indicates an altitude of about #i1hjj feet1 and that at the right1 that the exposure was made #g seconds after #aa ,a4,m4 ,the other symbols record that this photograph was ,no4 #ac of a series made at ,rochester1 ,n4 ,y41 ,october #bc1 #aibj1 with an ,eastman mapping camera known as ,k-#b4 ,the symbol #h-,p is non-essential and records that this negative is ,no4 #h of panchromatic film4 ,illustration3 ,,fig4 #b--,symbols of automatic register in the ,eastman mapping camera1 photographed with the body of the picture showing roads1 streams1 orchards1 cultivated fields1 etc4 ,for explanation of the symbols1 see the text4 ,the information given by the symbols is corroborated by the picture4 ,orchard and shade trees appear as circular dots in place of the elongated images characteristic of pictures taken obliquely downward1 and the short1 squat shadows denote exposure near midday4 ,shocks of corn standing in the fields show that the season is autumn4 ,,how ,,to ,,read ,,airplane ,,photographs ,not all the features1 however1 are so easily recognizable4 ,oblique photographs are often more readily interpreted than ordinary photographs1 since they combine with the usual view the essentials of a plan2 but in vertical photographs very few objects present an appearance that is natural in the light of our experience as lateral observers4 ,the uninitiated1 on attempting systematically to identify the features of a vertical photograph1 find a very large number that are foreign in appearance4 ,a necessary preliminary is an acquaintance with the ground photographed or with similar regions and features4 ,without such a key the air photograph is not always self-interpretative and is often unintelligible4 ,military observers are carefully trained to recognize features of military significance4 ,it is not to be expected1 however1 that they should be trained in the observation of land forms except such as are of military importance4 ,consequently1 whereas a great variety of photographs is now easily obtainable at many flying fields1 the information that a scientist would desire concerning them is not so easily available4 ,most of the photographs used in this paper were taken by men who were not trained in observing land forms4 ,many were taken simply as a requirement in practice flights and meant so little to the observer that no record was made concerning them4 ,for several not even the location was recorded4 ,it is of primary importance that the picture be held in the right position4 ,not only must the observer imagine himself looking directly down on the scene but he must hold the photograph in the position in which experience has shown that the image appears the most natural4 ,otherwise a depression will appear as an elevation and an elevation as a hollow4 ,it is a well-known fact that in telescopic photographs of the moon the craters appear like hollows when the print is held in one position and like elevations when the position is reversed4 ,experience shows that if the print is held so that the shadows fall toward the observer the objects appear natural4 ,the reason is that the observer sees only those shadows that are caused by light falling towards him4 ,consequently1 the only interpretation that the brain can give to shadows on a photograph is that they are cast by an elevation between the eye and the light4 ,in a picture1 therefore1 in which shadows fall away from the eye instead of towards it valleys are seen as hills and hills as valleys4 ,in the northern hemisphere this prescribed orientation conflicts with the convention of placing the north side of a map at the top of the page and also with the modern shaded map on which the light is represented as coming from the upper left1 or northwest1 corner of the map4 ,,failure ,,of ,,air ,,photographs ,,to ,,show ,,relief1 ,,and ,,measures ,,to ,,remedy ,,this ,,defect ,in photographs taken from the ground the lights and shadows are such that a high degree of naturalness is possible4 ,but objects seen from directly above1 and even those viewed obliquely1 though to a lesser degree1 are illuminated so uniformly that photographs of them are apt to appear flat4 ,to some extent this has been overcome by the use of extra-sensitive emulsions1 special ray filters1 and printing papers adapted for accentuating contrast4 ,many of the photographs used in this book did not allow satisfactory reproduction till the contrast of the negatives was greatly increased by the arts of the photographic laboratory4 ,but1 even at its best1 no photograph taken vertically affords an adequate idea of the height of hills or the depth of hollows4 ,only shadows that are particularly well defined can be distinguished as shadows1 while small elevations and depressions affect the negative no differently than a difference in marking or color4 ,in military defenses1 if the mere surface of the camouflage is sufficiently realistic1 the ordinary camera is even more easily deceived than the human eye4 ,it is a well-known fact that man and other animals of the higher order see objects in relief1 within a certain range of vision1 because the eyes convey to their respective retinas slightly different images of the same object which the brain combines into a relief image4 ,the stereoscopic camera has long been used for the same purpose4 ,its principle1 with certain adaptations that need not be discussed here1 has been to some extent employed in airplane pictures1 with such excellent results that it is claimed by some that by further development actual contouring will be possible by this means4 ,it is reported that in military reconnaissance stereoscopic pictures render ordinary camouflage useless and that bridges1 observation towers1 gun emplacements1 etc41 are shown in relief and1 therefore1 easily detected4#b ,,chapter ,,ii ,,familiar ,,scenes ,,from ,a ,,new ,,angle 7,,figs4 #a1 #c1 ,,and #d7 ,pictures of well-known buildings are of wide appeal4 ,in so far as they create an interest in the activities for which the buildings stand they are distinctly educative4 ,such widely known buildings as the ,national ,capitol and the ,library of ,congress are used repeatedly for illustration4 ,they are as welcome as the sight of a familiar face4 ,any unusual circumstance connected with them is seized upon as an excuse for republishing pictures of them4 ,views of them from a new angle are always in demand4 ,not only do air photographs offer a welcome novelty1 but they have the added advantage of lifting the subject out of the clutter of surrounding buildings and making it really the central figure of the picture4 ,it would be difficult to get a more impressive view of the ,national ,capitol than that of ,figure #a or a more attractive glimpse of the ,naval ,academy at ,annapolis than that of ,figure #d4 ,the objects of chief interest occupy the center of view without distracting obstructions4 ,in the former1 the imposing structure of the ,capitol building appears in a pleasing setting of minor details4 ,the proximity of the ,senate ,office ,building and the ,library of ,congress is at once apparent1 and the radiating systems of the avenues of approach4 ,strangers may have wondered as to the nature of the environs of the ,capitol4 ,the tree-lined streets and the apartment houses seen in the picture answer the question4 ,in the view of the ,naval ,academy the buildings occupy the center of the scene1 with the beautiful dome of the memorial to ,john ,paul ,jones1 the first great ,american naval fighter1 prominently in view4 ,spa ,creek in the foreground1 a part of the capital city of ,maryland at the left1 and the ,severn ,river1 with its low wooded banks1 stretching away ,illustration3 ,,fig4 #c--,west ,point1 ,n4 ,y41 and the ,hudson ,river4 ,an air view of the ,united ,states ,military ,academy and the gorge of the ,hudson4 ,the picture shows the commanding view of the river to be had from the point of land #ahj feet above the river on which the ,military ,academy is located and shows the wisdom of the choice of this spot as one of the chain of redoubts by which the river was fortified during the ,revolution4 ,illustration3 ,,fig4 #d--,the ,naval ,academy at ,annapolis1 ,md4 ,oblique view from an airplane from a position over ,eastport in a general northwesterly direction4 ,the water in the foreground is ,spa ,creek4 ,the ,severn ,river1 spanned by the county bridge and the ,baltimore and ,annapolis ,railroad bridge1 stretches away to the left4 ,the buildings in the middle of the picture are those of the ,naval ,academy4 ,the domed mausoleum built in honor of ,john ,paul ,jones1 which serves as his final resting place1 appears at the left4 ,still farther to the left lies ,maryland's capital city4 ,of interest is a comparison of the low-lying and stream-cut banks of the drowned valley now occupied by the ,severn ,river with the mountains through which the ,hudson ,river has cut its gorge at ,west ,point 7see ,fig4 #c74 in the distance1 spanned by the county bridge and the ,baltimore and ,annapolis ,railroad bridge1 form an interesting setting and show1 without detracting from the importance of the academy itself1 its advantageous location with regard to the city and the water approaches4 ,,chapter ,,iii ,,architecture1 ,,landscape ,,gardening1 ,,and ,,engineering 7,,figs4 #e ,,to #ad7 ,only a few photographs are necessary to show how valuable to the architect1 the construction engineer1 the city planner1 or the landscape gardener the air photograph1 both vertical and oblique1 is destined to become4 ,pictorial records of progress in the construction of buildings1 bridges1 ships1 canals1 reservoirs1 etc41 that partake also of the nature of ground plans1 as do air photographs1 furnish an admirable means of study and comparison4 ,no photograph of the great shipyards at ,newport ,news taken from the ground would show the relation of the shops and drydocks to the deep-water approaches as does ,figure #g4 ,figure #h gives an unusually comprehensive idea of the location1 magnitude1 and construction of ,hell ,gate ,bridge2 and ,figure #aj1 ,rockaway ,beach1 now a densely populated town where a few years ago was a barren strip of sand1 suggests that photographic records of construction in rapidly growing communities where changes are being made in streets1 railroads1 and buildings1 will come to be a part of the equipment of the city engineer and architect4 ,,architecture ,,and ,,landscape ,,gardening ,equally useful will the air photograph become to the landscape gardener and architect4 ,heretofore1 in order to get a comprehensive conception of his task and a definite picture of its completion1 the landscape gardener has had to depend upon the use of maps and such views as could be made by the sketch artist or the ordinary lateral photograph4 ,in the future1 from vertical and oblique photographs of the area to be developed1 he will have the means of studying its features in their correct proportions and relationship4 ,by means of similar photographs of completed projects he can choose and combine until he has developed the plans best suited to his purpose4 ,he can bring to his aid first-hand studies of gardens and grounds the world over whose beauties have made them famous4 ,illustration3 ,,fig4 #e--,monument ,avenue1 ,richmond1 ,va41 and the statue of ,robert ,e4 ,lee4 ,an oblique photograph illustrating the use of aerial photography in landscape gardening and street planning4 ,,engineering ,,projects ,,covering ,,large ,,areas ,where the project covers large areas1 the 8mosaic10 or group of matched photographs1 can be used in the study of problems of construction or improvement4 ,figure #ac1 a mosaic of the ,anacostia flats1 the site of improvements under way in the ,district ,illustration3 ,,fig4 #f--,the ,united ,states ,naval ,observatory and grounds1 ,washington1 ,d4,c41 as seen from an airplane at a height of a few hundred feet above the ground1 showing an unusually attractive arrangement of shrubbery and trees4 of ,columbia1 shows the ,anacostia marshes as they appeared in the autumn of #aibj1 after the changes effected since #aiae1 as can be seen by comparison with ,figure #ad1 the topographic map of the same area4 ,to the right is the terraced slope rising to a height of about #aej feet above the river--an elevation so low that the air photograph does not properly reproduce it4 ,near the foot of the principal terrace lie the tracks of the ,pennsylvania ,railroad1 on which can be seen ,benning1 ,deanewood1 and ,kenilworth4 ,between the railroad and the ,anacostia ,river are the ,benning race track and the swampy lowland and tidal marshes of the ,anacostia flats4 ,the river and the marshland on either side of it from the ,pennsylvania ,avenue ,bridge to ,benning ,road have been modified by dredging1 but north of ,illustration3 ,,fig4 #g--,shipyards at ,newport ,news1 ,va41 showing docks and deep-water approaches1 steamships1 and drydocks1 in one of which is a vessel for repairs4 ,illustration3 ,,fig4 #h--,the ,new ,york ,connecting ,railroad ,bridge1 which affords an all-rail passenger and freight route between ,boston and ,washington4 ,the bridge1 which was completed in #aiag1 starts on the mainland in the ,port ,morris section of southern ,bronx ,borough1 ,new ,york ,city1 seen in the background1 then crosses ,bronx ,kill1 ,randalls ,island1 ,little ,hell ,gate1 ,wards ,island1 and ,hell ,gate to reach the ,long ,island shore1 seen in the extreme lower right corner1 at ,long ,island ,city1 ,queens ,borough4 ,the tracks continue towards ,washington by way of tunnels under the ,east ,river and the ,hudson4 ,illustration3 ,,fig4 #i--;,a part of ,washington1 ,d4,c41 showing the ,white ,house1 ,treasury1 ,state-,war-,navy1 and other public buildings in the foreground2 the ,ellipse1 ,washington ,monument1 and new ,war and ,navy offices in the middle ground2 and the ,tidal ,basin1 ,potomac ,park1 and the ,potomac ,river in the distance4 ,by no other means could so informative a glimpse be given of a spot of such wide interest4 ,every feature in the picture is more or less familiar to a large number of ,americans1 but their familiarity is with the individual features rather than with their situation and relation to one another as shown here4 ,illustration3 ,,fig4 #aj--,part of ,rockaway ,beach1 ,long ,island1 ,n4,y41 showing city blocks1 streets1 and buildings covering the sand which a few years ago was barren and unoccupied4 ,scale1 about #a3 #f1gjj4 ,illustration3 ,,fig4 #aa--,landscape gardening4 ,an airplane view of a part of ,long ,branch1 ,n4,j41 taken from a height of #aj1jjj feet1 showing the beach and surf at the right1 and the streets1 mansions1 driveways1 and lawns in the body of the picture--an example of the development of a barrier beach of little value before the exploitation for summer homes4 ,scale1 about #a3 #ae1jjj4 this road the surface appears in its natural state4 ,in the mosaic are shown at the left the highlands west of the marshes1 wooded in some places but cleared and improved in others4 ,in the northern part can be seen land wooded north of the ,district line but cleared south of it4 ,so comprehensive a view of the field of the project and of the progress to date should be of great service to the engineers and promoters4 ,,chapter ,,iv ,,the ,,mosaic 7,,figs4 #ac ,,and #bb7 ,in its simplest form1 the mosaic is made by mounting overlapping prints so that the corresponding details coincide4 ,this type of mosaic is quite adequate for relatively small areas or where a high degree of accuracy is not required4 ,for larger areas and greater accuracy1 an accurate outline map is used as a base upon which the prints are mounted so that recognizable features coincide with their location on the map4 ,when the prints are properly arranged1 the better print of each overlapping pair is selected1 the excess paper removed1 and the whole mounted and photographed4 ,figure #ac is left untrimmed to illustrate the method of matching the overlapping prints4 ,the differences in shade are due to difference in printing and developing the pictures which make up the mosaic4 ,the slight offsetting of line at the junction of the prints may be due to errors in mounting1 shrinking1 or stretching of the photographic paper1 tilting of the camera at the time of exposure1 or other cause4 ,such errors and imperfections illustrate the difficulty of using these photographs in the making of maps4 ,a skillful manipulation of both airplane and camera is necessary to the success of the mosaic4 ,to prevent distortion and variation of scale1 the camera must be maintained at the same altitude at all times and pointed directly downward4 ,this can be accomplished by flying with an even keel at a uniform altitude4 ,mechanical devices are also being perfected to accomplish the same result4 ,still greater skill is necessary when consecutive rows of exposures are made for the purpose of placing strips of photographs side by side to cover a large area4 ,it is difficult under the varying conditions of wind and weather to fly so evenly and so nearly at the same level that distortions and differences in scale are not noticeable4 ,strong objection to the mosaic is frequently raised because of inaccuracies due to difference in scale in neighboring prints4 ,until these defects are overcome1 such a group of matched photographs cannot take the place of an accurate map4 ,much1 however1 is being done to correct these defects1 and1 even in photographs where inaccuracies in scale are many1 the value of the photograph for the portrayal of detail cannot be denied4 ,,chapter ,v ,,general ,,aspects ,,of ,,the ,,surface ,,as ,,seen ,,from ,,the ,,air 7,,figs4 #ab ,,to #ah7 ,illustration3 ,,fig4 #ab--;,benning1 ,d4,c41 and the ,anacostia ,river1 showing1 from right to left1 cultivated lands #dj to #bj feet above sea level1 an elevation too slight to be shown in a vertical photograph2 a brushy slope running from #bj feet to sea level2 and marshland along the stream4 ,the checkered pattern of the upland fields is caused by different-colored crops4 ,shocks of corn1 spaced evenly in rows1 buildings and shade trees1 and light-colored roads and a race track are shown4 ,the light-colored areas along the stream are occupied by tidal marsh and are free from brush but covered with vegetation of annual growth4 ,the figure is one of the photographs used to make the mosaic shown on ,fig4 #ac4 ,it should be compared with ,fig4 #ac and with the topographic map1 ,fig4 #ad4 ,scale1 #a3 #aa1jjj4 ,when a region is viewed from an altitude of several thousand feet the observer can readily imagine himself looking down on a large map4 ,the chief features stand out prominently1 the smaller to a lesser degree4 ,mountains1 rivers1 and the seashore are ,illustration3 ,,fig4 #ac ,illustration3 ,,fig4 #ad ,illustration3 ,,fig4 #ac--,vertical photograph of the land along the ,anacostia ,river on the eastern edge of ,washington1 ,d4,c41 made up of several photographs matched together and adjusted to points located by ordinary survey methods1 and reduced in size to correspond with the map1 ,fig4 #ad4 ,the photographs were taken from an airplane with a so-called mapping camera at such intervals of time that the prints overlap1 thus making it possible to adjust them to each other and to form a continuous picture of the area4 ,the region shown is the site of improvements that are at present under way1 mainly the regulation of the ,anacostia ,river4 ,the channel has been widened by dredging and part of the bordering marsh areas filled in4 ,the photograph shows that this work had progressed to the ,benning ,road bridge by the autumn of #aibj1 when the photograph was taken1 while in #aiae1 when the area was surveyed for the map1 it had been carried out only as far as the ,pennsylvania ,avenue bridge4 ,such airplane photographs furnish an incomparable tool in the handling of large-scale engineering projects1 both in the study of the territory in its unimproved state and to follow the progress of the work after operations are under way4 ,scale1 about #a3 #bh1jjj4 ,illustration3 ,,fig4 #ad--,part of the topographic map of ,washington and ,vicinity1 #a3 #ca1fhj1 published by the ,u4,s4 ,geological ,survey1 showing within the irregular line the same area shown in ,fig4 #ac4 ,scale1 #a3 #bh1jjj4 ,illustration3 ,,fig4 #ae 7on page #bd7--,mosaic of the southeastern part of ,mulberry ,island1 on the left bank of the ,james ,river about #aa miles northwest of ,newport ,news4 ,va41 showing an area portrayed by many photographs matched together4 ,slight differences in shade indicate the junction of the separate prints4 ,the higher land1 about #aj feet above sea level as determined by surveys on the ground1 is shown at the right by roads and cultivated fields4 ,it is to be noted that roads outline the dividing line between the high ground and the marsh4 ,at the left are lower areas of wooded or brushy swampland and of grassy marsh4 ,they contain a number of abandoned channels3 some completely silted up1 others containing small thoroughfares1 and still others drained by meandering streams which seem to have developed after the channels were definitely abandoned by the streams which originally occupied them4 ,the streams which drain the marshes have many characteristics of streams which drain higher lands4 ,they have dendritic patterns1 so called from resemblance to the forking branches of a tree2 channels which widen downstream2 and winding or meandering courses4 ,the island terminates in a long spit composed of silt and fine sand4 ,the banks to the left on ,james ,river are low and marshy3 those to the right on ,warwick ,creek1 except for one small marsh1 form low bluffs4 ,in order that the mosaic may be compared with the map1 ,fig4 #af1 it has been placed with the northerly part at the top of the page1 with the result that1 until the page is reversed1 the trees in the swampland appear like hollows in the earth4 ,scale1 #a3ad1jjj4 especially conspicuous4 ,streams appear as smooth1 winding ribbons--glistening if the sunlight reflected from them enters the eye1 dark if the bright rays are reflected away from the eye4 ,railroads can easily be traced and towns recognized by their form4 ,concrete roads and others of light-colored material are plainly visible4 ,those built of dark-colored material appear less prominently4 ,something even of the character of the forests can be ascertained--whether evenly timbered or partly of primary and partly of secondary growth2 whether intact or partly burned over2 whether consisting chiefly of one species of trees or of many4 ,the cultivated fields and their relations to roads1 streams1 and forests are conspicuous4 ,towns and cities are spread out like panoramic views in which are strikingly visible the residence and manufacturing centers1 the layout of streets1 the systems of parks1 the position of suburbs1 and the relation of these to routes of transportation and travel--roads1 railroads1 and waterways4 ,these and many other features of the landscape--swamps1 marshes1 buildings1 trees1 orchards1 and many lesser details--are recognizable and are all recorded on the ,illustration3 ,,fig4 #ae4 7,for explanation1 see p4 #bc47 ,illustration3 ,,fig4 #af--,the same area as shown in ,fig4 #ae reduced from a section of a map on the scale of #a3aj1jjj by the ,corps of ,engineers1 ,u4,s4,a4 ,the photographs shown in ,fig4 #ae were used for mapping certain small features on this map1 such as small streams4 ,scale1 #a3ad1jjj4 photographic negative4 ,so faithfully does the camera reproduce all the horizontal features within its range of vision that it is conceivable that a photograph correctly dated might become a valuable record in cases of boundary disputes or other litigations involving the position of fences1 fields1 roads1 or even streams1 at a given date4 ,illustration3 ,,fig4 #ag ,illustration3 ,,fig4 #ah ,illustration3 ,,fig4 #ag--;,columbus4 ,ga4 ,a part of a mosaic made at ,camp ,benning near-by in #aiji showing the town1 river1 and surrounding country4 ,the scale is so small that buildings and trees appear as dots1 city blocks as small parallelograms1 streets and roads as light-colored lines4 ,the cultivated fields appear as irregularly checkered areas1 and the concentric lines of the terraced slopes have the appearance of contour lines on a topographic map 7see ,fig4 #ah74 ,the picture illustrates many of the features of city geography4 ,the comparatively straight course of the river and the heavy growth of trees and bushes along its edges indicate a minimum of flood-plain and steep banks--an inference supported by the fact that the principal business center of the city1 shown by large1 closely set roofs1 is built close to the river4 ,surrounding this section is the most densely populated district1 which in the northern part of the city gives way to a district of houses set farther apart and separated by lawns set with trees4 ,other less extensive business centers are shown as small spots of closely grouped buildings4 ,a variety of suburban types is to be seen3 some quite city-like1 with a business center1 a densely populated residential district1 and a district of houses separated by grounds2 others more village-like in their lack of a well-developed center but still more or less completely separated from the city proper2 still others1 sporadic scatterings of houses and grounds extending from the city for some distance along the principal roads4 ,the railroad center is located conveniently near the business center1 and the radiating lines of road and railroad communications are in strong contrast to the rectangular arrangement of the city streets4 ,factories1 indicated by large1 light-colored roofs1 are located along the railroad in the southern part of the city and along the river to the north4 ,those along the river are operated by power from the falls which the picture shows4 ,the terraced slopes are characteristic of the region1 the farmers here and elsewhere in the ,south making these terraces in their plowed fields to prevent rain water from washing away the soil4 ,scale1 about #a3ch1jjj4 ,illustration3 ,,fig4 #ah--,map of the same area shown in ,fig4 #ag enlarged from the corresponding sections of the #a3fb1ejj ,columbus and ,seale1 ,ga4-,ala41 and the #a3abe1jjj ,talbotton and ,opelika1 ,ga4-,ala41 topographic sheets surveyed mainly in #aijf and #aijg and published by the ,u4,s4 ,geological ,survey4 ,the cross section at the bottom lies along the line indicated on the map and extends somewhat beyond the right border of the map4 ,the section shows the broad shelf upon which the city rests and its relation to the river and to the terraced hillsides east of it4 ,scale1 #a3ch1jjj4 ,,chapter ,,vi ,,marshes ,,and ,,marsh ,,drainage 7,,figs4 #ai ,,to #bg7 ,mention has been made of the objects seen better from the air than from any viewpoint on the ground2 but there are some objects which as a whole can be seen only from above4 ,swamps1 parts of everglades1 peaks in the midst of difficult country1 precipitous canyon walls1 and many volcanic craters cannot be seen from the ground without undue effort4 ,photographs of bluffs1 terraces1 and other slopes facing bodies of water have hitherto been adequately obtainable only from the water4 ,all of these can be readily viewed and photographed from the airplane4 ,pictorial representations of drainage systems were rare until photographs such as ,figure #ai were taken from airplanes4 ,the intricate drainage of marshes like those along the ,pamunkey ,river in ,virginia pictured in ,figure #bj was never accurately shown until photographed from the air4 ,of frequent occurrence on the ,atlantic ,coastal ,plain of the ,united ,states are swamps and marshes inaccessible from the ground4 ,much of the surface material is so soft that they cannot be easily traversed2 and1 even where firm enough to support a man's weight1 few of the details are deemed of sufficient importance to warrant the trouble and expense of mapping by ordinary methods4 ,yet the trapper would scarcely admit that these details are unimportant1 and1 to the student1 they are an interesting feature of marsh topography that has thus far received little attention4 ,figure #be is part of the excellent ,new ,kent1 ,va41 sheet of the topographic map and is probably as detailed as a map of this character should be when made from ground surveys only4 ,however1 on comparison of the map with a photograph of the same area 7,fig4 #bd71 there is no difficulty in detecting errors2 and it is probable that1 had the photograph been available when the map was made1 the marshes would have been represented differently4 ,illustration3 ,,fig4 #ai--,stream development in a tidal marsh1 showing1 at the right1 the northern end of ,ludlam ,beach1 about #f miles south of ,ocean ,city1 ,n4,j41 and the mouth of ,corsons ,inlet leading to ,ludlam ,bay1 and1 at the left1 the marsh just west of the inlet1 with streams rising close to the bank of the larger stream at the extreme left and flowing in meandering courses across the marsh4 ,the great variety of types of vegetation probably is one cause of the remarkable meandering of these drainage lines by reason of the fact that the accumulated remains as well as the annual growth of different weeds and grasses offer varying resistance to the current of the streams4 ,scale1 about #a3aj1jjj4 ,,marsh ,,drainage ,one of the most striking characteristics of marsh topography illustrated by the photographs presented here is the great wealth of drainage lines and the resemblance of the drainage patterns to those of river systems developed on higher ground4 ,the dendritic patterns1 the meanders1 and the sharply outlined divides are surprising in areas which have altitudes varying from only a few inches to a little more than a foot at times of ordinary high tide and which are wholly submerged at times of maximum tide4 ,some of the streams have gently winding courses suggestive of normal stream development4 ,others1 particularly the smaller1 have a conspicuous angularity of course4 ,it is possible that the latter may have originated as the trails of animals4 ,some of the lines are observed to cross the larger streams and are probably tracks made by muskrats4 ,some of the streams rise close to the river's brink and lead to through-going waterways near the center of the marsh4 ,this suggests the deposition of silt on the brink of the river at times of high water4 ,the notched appearance of the shore in ,figure #bj seems to be due to overhanging bunches of sedge grass and1 in some instances1 to the breaking away of the surface mat or crust of the marsh formed by the interlacing roots of grass4 ,the mottled appearance of the marsh in this picture may be partly due to shadow of clouds1 but to some extent1 at least1 the difference in shade is caused by differences in the character of the plants4 ,the marshes used for illustration here are typical of many along the ,atlantic ,coast4 ,they are situated near ,west ,point1 ,va4 ,the ,pamunkey and the ,mattaponi ,rivers both rise in the ,piedmont ,plateau1 flow southeastward through the tidewater portion of ,virginia1 and join about midway of the ,coastal ,plain to form the ,york ,river#c 7see ,fig4 #eh74 ,illustration3 ,,fig4 #bj--;,details of marshland4 ,a part of ,lee ,marsh near ,west ,point1 ,va4 7cf4 ,fig4 #bf71 as photographed from a height of #b1jjj feet1 ,june1 #aibj4 ,local observers report that this marsh has been submerged only twice in nineteen years4 ,the drainage systems are well entrenched4 ,the larger stream channels are cut #a to #e feet or more below low tide 7the tidal variation at ,west ,point is about #c4d feet71 and their form is made stable by the tough surface crust of the marsh1 consisting of the matted roots of the luxuriant sedge grass4 ,the intricate1 veinlike appearance of the drainage lines and the furry appearance of the edges of all the waterways1 showing overhanging vegetation1 are of interest4 ,drainage systems flowing in opposite directions slow connecting tributaries apparently silted up4 ,scale1 about #a3d1jjj4 ,illustration3 ,,fig4 #ba--;,details of frequently submerged marshland4 ,a part of ,cousaic ,marsh on the ,pamunkey ,river1 near ,sweet ,hall1 ,va4 7cf4 ,fig4 #bd71 as photographed from a height of #b1jjj feet1 ,june1 #aibj4 ,the surface of the marsh is covered with water several times each year1 according to local report4 ,it is relatively soft1 and a comparison with ,fig4 #bj shows an apparently different1 less dense vegetation than that of ,lee ,marsh1 which is rarely submerged4 ,the stream channels are less definitely fixed and lack the evidence of overhanging vegetation4 ,scale1 about #a3d1jjj4 ,illustration3 ,,fig4 #bb--;,atlantic ,city and ,ocean ,city1 ,n4,j4 ,strips of photographs taken from an airplane1 ,march1 #aibj1 from a height of #aj1jjj feet1 showing1 in order from east to west3 the ocean water1 which appears dark-colored2 the surf1 white where it breaks into foam2 the light-colored beach sand2 the cities laid out on the sand of the barrier beach2 and the marshes1 channels1 and drainage systems west of the barrier4 ,west of ,peck ,beach in the strip of photograph at the right many features characteristic of salt marsh areas of the ,coastal ,plain are shown back of the barrier beach4 ,the right strip forms the southern continuation of the left strip4 ,scale1 about #a3ge1jjj4 ,illustration3 ,,fig4 #bc--;,a river system in miniature4 ,a small stream near ,hampton1 ,va41 showing flood plain1 meanders1 an ox-bow lake and cut-off1 abandoned channels and a delta partly under water4 ,scale1 not known4 ,illustration3 ,,fig4 #bd--,sweet ,hall ,marsh on the lower ,pamunkey ,river1 near ,west ,point1 ,va41 as photographed from a height of #aj1jjj feet at #aa ,a4,m41 ,december #aa1 #aibj4 ,cousaic ,marsh lies to the left and ,hill ,marsh to the right of the central meander4 ,some of the watercourses in these marshes are thoroughfares1 or channels opening to the river at both ends1 that can be traversed by boat at high tide4 ,but many of them are quite different in nature1 beginning as minute rills and broadening toward the mouth in a manner suggesting typical drainage channels on higher land4 ,scale1 about #a3ca1jjj4 ,illustration3 ,,fig4 #be--,the same area as shown in ,fig4 #bd1 enlarged from the ,new ,kent1 ,va41 topographic sheet1 #a3fb1ejj1 published by the ,u4,s4 ,geological ,survey4 ,the cross section at the left lies along the line indicated on the map and extends somewhat beyond its borders4 ,the somewhat greater height of the map than of the photograph1 although both cover exactly the same area1 is due to the unavoidable slight difference in tilt of each of the exposures of which the photographic mosaic is made up4 ,this illustrates the fact that airplane photographs cannot be directly used as equivalent to maps1 until the necessary adjustments have been made4 ,experiments in camera construction are under way to overcome these difficulties by automatic devices4 ,scale1 #a3ca1jjj4 ,illustration3 ,,fig4 #bf--;,eltham ,marsh on the lower ,pamunkey ,river1 as photographed from an altitude of about #aj1jjj feet at #aa ,a4,m41 ,december #aa1 #aibj4 ,at the right lies the town of ,west ,point1 ,va41 at the junction of the ,mattaponi and ,pamunkey ,rivers1 and at the left appears a part of ,lee ,marsh4 ,eltham ,marsh1 in the center of the illustration1 is traversed by a so-called thoroughfare1 through which boats of light draft make their way at high tide4 ,at one point in the middle of the marsh the thoroughfare is perceptibly broader than elsewhere1 and the tidal currents entering from opposite ends of the thoroughfare meet there and cause slack water in which silt is deposited1 forming mud flats exposed at low tide4 ,the cultivated fields south of the marsh are on a bench about #aj feet higher than the marsh4 ,scale1 about #a3ca1jjj4 ,illustration3 ,,fig4 #bg--,the same area as shown in ,fig4 #bf1 enlarged from the ,new ,kent1 ,va41 topographic sheet1 #a3fb1ejj1 published by the ,u4,s4 ,geological ,survey4 ,it is obvious that many interesting details shown by the photograph are missed or neglected as unimportant in the most careful mapping4 ,the cross section at the left lies along the line indicated on the map and extends somewhat beyond its borders4 ,scale1 #a3ca1jjj4 ,the ,york is one of the estuaries of the tidewater portion of ,virginia1 and the water level at ,west ,point1 the junction of the two tributaries1 rises and falls about #c feet under tidal action4 ,the ,pamunkey is affected by the tide #ec miles by channel above ,west ,point1 and the ,mattaponi #db miles4 ,much of the broad lowland along these rivers is marshy1 but the largest marshes are found near ,west ,point1 where the river current in swinging from side to side has formed great meanders4 ,for some reason the valleys eroded long ago by these streams have filled with sediment here to a greater extent than farther downstream2 perhaps because this is essentially the head of sea water1 so that the checking of the current of the river causes it to deposit much of its load4 ,sea water regularly mingles with the river water as far upstream as ,west ,point1 but above this point the water is chiefly fresh4 ,the marshes consist of soft mud and muck to a considerable depth4 ,a well driven in ,hill ,marsh to an underlying artesian horizon penetrated #ej feet of this soft material before entering rock such as is exposed in the river bank4 ,the thickness of the mud is comparable to the maximum depth of the ,york farther downstream and suggests that the old valley which there is filled with water is here filled to a depth of #ej feet or more with sediment brought down by the river4 ,only a small part of the marsh near the landward margin has surface material firm enough to support the weight of large animals except when the surface is frozen4 ,many kinds of marsh plants grow here1 among which is sedge grass 7,spartina cynosuroides 7,l47 ,willd471 which grows to a height of #aj feet or more and forms dense thickets4 ,its roots interlace to form a tough mat which in some places will support the weight of a man4 ,in other places the soft muck reaches to the surface4 8,,thoroughfares0 ,these marshes are cut by a few waterways open at both ends1 known as thoroughfares1 or tidal runs1 which also serve as the trunk streams through which the marsh is drained4 ,some of the thoroughfares may be trunk streams modified by tides1 or they may be silted remnants of abandoned river channels4 ,some seem to be channels in the last stages of silting4 ,the incoming tide enters the down-river end but ascends the thoroughfare more slowly than it ascends the river4 ,the tide in the river reaches the upper end of the thoroughfare1 enters it1 and meets the opposing tide within the marsh near the upstream end of the passageway4 ,where the tides meet1 thus causing slack water1 silt is deposited and mud flats are formed4 ,in ,eltham ,marsh 7,fig4 #bf7 these flats are well within the marsh4 ,in the larger thoroughfares of ,sweet ,hall ,marsh 7,fig4 #bd7 the tide passes entirely through while the tide in the river is making its long way around1 so that slack water and the deposition of silt occur at the extreme upper end of the passage4 ,in all of the thoroughfares the silting has reached the stage that precludes their use by boat1 except at times of high water4 ,even at high tide some are navigable only by small skiffs1 although throughout much of the course the water is many feet deep4 ,some of the thoroughfares become narrow and shallow upstream in a manner that suggests that they originate as two normal streams flowing in opposite directions from a common point and that they were later united by the breaking down of the divide between their headwaters4 ,such a junction might be affected by an unusually high tide breaking through a divide and cutting a channel4 ,such a divide1 be it noted1 consists of soft mud only a few inches above the general level and might readily be broken down4 ,in some instances the connection may have originated as an animal trail1 as we have seen4 ,muskrats1 otters1 and other marsh animals use the waterways as lines of travel and make paths in between them from one to another4 ,apparently many of the small drainage lines originated in this way1 but in some instances stream systems of considerable size and complexity are independent of all others and possess all the characteristics of normally developed river systems4 ,,chapter ,,vii ,,coastal ,,mud ,,flats 7,,figs4 #bh ,,and #bi7 ,of frequent occurrence along the ,atlantic ,coast of the ,united ,states are low mud flats which are practically at sea level and which are covered with water at times of high tide4 ,where these tracts are exposed to the air during ebb tide for so short a time that plants have not taken root and where the surface material is fine-grained and soft1 the tracts are known as mud flats4 ,in the part of the peninsula between ,delaware and ,chesapeake ,bays belonging to the state of ,virginia which is called the ,eastern ,shore a low barrier beach of sand has formed on the ocean side several miles off shore1 and the space between this and the mainland is occupied by mud flats1 broad1 shallow lagoons1 and an intricate maze of interlacing channels and winding1 branching1 interlocking1 vermicular streams4 ,the mud flats are exposed for a short time during low tide1 and1 as the surface of the water here rises and falls with the tide more than #d feet1 with a maximum fluctuation considerably greater1 large volumes of water are continually flowing backward and forward over the flats4 ,as the tide rises1 strong currents of sea water set in through the inlets1 flow up the main channels and through the thoroughfares1 and gradually find their way into the countless small channels and out of them over the broad level stretches of soft mud4 ,as the tide falls1 this action is reversed1 and the broad sheet of water finds its way by devious paths through the winding watercourses out to sea4 ,the larger channels extend considerably below the surface at times of highest water and may be quite deep even at times of low water4 ,they are1 perhaps1 stream courses excavated before the region was drowned4 ,many of the smaller channels also have the general form characteristic of normal stream channels1 although others show peculiarities not common to subaerial drainage4 ,the origin of these submarine and tidal features is not well understood1 but the photographs of them show their form and furnish some basis for a study of them4 ,illustration3 ,,fig4 #bh--;,a stream system of the mud-flat area on the ocean side of the ,eastern ,shore1 ,virginia4 ,the light-colored area is beach sand above water4 ,the treelike form is a stream system of subnormally developed pattern4 ,note the seeming uncertainty of course1 some of the branch streams rising close to the mouth of the trunk stream2 the junction of branches at the head2 and the 8frostwork0 patterns4 ,scale not known4 ,illustration3 ,,fig4 #bi--,mud-flat streams1 showing curious frostwork pattern at the head of underwater channels4 ,note the pools and the veinlike drainage lines from them4 ,scale not known4 ,the photographs reproduced as ,figures #bh and #bi were taken northeast of ,cape ,charles1 ,virginia1 in the summer of #aibj at low tide4 ,the light-colored ribbon-like bands represent water-filled channels2 and the darker-colored areas1 either wet mud exposed to the air or mud slightly submerged4 ,however1 photographs taken under certain conditions of light may show the exact line between the exposed and the drowned portions of a land surface4 ,,chapter ,,viii ,,submerged ,,land ,,forms 7,,figs4 #cj ,,to #cc7 ,heretofore the study of beaches1 deltas1 and other partly submerged land forms has been chiefly confined to the exposed parts1 the underwater forms being largely matters of conjecture4 ,by means of air photographs not only can the exposed parts of the delta and beach be studied1 but the forms of shoals and terraces1 the underwater portions of river deltas1 tidal deltas and their underwater distributaries1 and many other submerged forms can be shown clearly4 ,sand bars1 terraces1 and other submerged forms appear in many of the photographs already presented2 but a few so taken that the bars and terraces appear to be the chief objects in the picture may be useful for illustrating the underwater land forms and for demonstrating that these forms can be successfully photographed4 ,unfortunately not many photographs could be found which were taken with the express object in view of illustrating underwater land features4 ,in most of the available photographs these features were only incidental1 the chief purpose in taking them being to photograph the shore4 ,much has been written concerning the physiographic history of the ,atlantic ,coastal ,plain of the ,united ,states1 and the question is still being debated whether the land is rising1 sinking1 or stationary4 ,to some extent these questions are answered by the exposed land forms4 ,the submarine forms are imperfectly known4 ,the possibility of recognizing shoals and channels from a photograph and of determining in some measure the shapes of the submerged land forms opens a new avenue of approach to the study of submarine geography4 ,in some places1 especially in regions of drowned topography1 it is possible that1 by using the air photograph in working out the physiographic processes that have produced the land forms that are now under water1 some of the vexing problems of earth history may be solved4 ,illustration3 ,,fig4 #cj 7left7--,sand bars and drowned terrace about ,stove ,point ,neck1 at the mouth of the ,piankatank ,river1 ,virginia1 as photographed from a height of about #aj1jjj feet at #aa3cj ,a4,m41 ,december #aa1 #aibj4 ,west 7left7 of the neck1 at the outer edge of the terrace1 the water is #b to #c feet deep at low tide1 or #e4g feet and #f4g feet at high tide1 but deepens abruptly westward1 where it is #bj to #cj feet deep in ,fishing ,bay 7see ,fig4 #cb74 ,to the south and east of the point the abrupt descent is at the side of the deep channel of the ,piankatank ,river4 ,to the right1 the bottom1 having a wavy appearance because of sand bars1 fades off more gradually under deep water4 ,the mottled area in the middle of the neck is wooded1 and the smoother parts near the point and in the upper part of the neck are cleared land4 ,scale1 about #a3cj1jjj4 ,illustration3 ,,fig4 #ca 7right7--,drowned terraces at ,gwynn ,island at the mouth of the ,piankatank ,river1 ,virginia1 as photographed from a height of about #aj1jjj feet at #aa3cj ,a4,m41 ,december #aa1 #aibj4 ,at the right is a part of the island1 showing trees1 fields1 and houses4 ,bordering the land area is a narrow band of light-colored beach sand1 expanded at ,cherry ,point into a conspicuous sharply recurved hook4 ,under the shallow water can be seen wave marks resembling large ripple marks4 ,the water is #b to #c feet deep at low tide at the outer edge of the light-colored submerged shelf1 beyond which the bottom descends abruptly toward the left to a depth of about #bj feet4 ,north of ,cherry ,point the waxy bottom shades off more gradually to the deep channel of the ,piankatank4 ,scale1 about #a3cj1jjj4 ,,the ,,best ,,conditions ,,for ,,photographing ,,underwater ,,land ,,forms ,illustration3 ,,fig4 #cb--,part of the ,kilmarnock and ,mathews1 ,va41 topographic sheets1 #a3fb1ejj1 published by the ,u4 ,s4 ,geological ,survey1 showing the location of ,figs4 #ca and #cb2 and a cross section along the line indicated on the map1 showing a terrace #bf feet above sea level at the left1 one less than #e feet above water level on ,gwynn ,island1 one #e feet or less below water level2 and the river channel with abrupt banks between the shoals4 ,scale1 #a3gj1jjj4 ,the photographic study of underwater land forms is relatively new1 and little information concerning it is available4 ,it is annoyingly obvious to the air observer that at times he can see nothing beneath the surface of the water1 whereas at other ,illustration3 ,,fig4 #cc--;,a drowned valley3 ,lambs ,creek1 #h miles southeast of ,yorktown1 ,va41 one of the estuary-streams tributary to ,chesapeake ,bay1 showing the broad mouth narrowing upstream and the irregular margins caused by partial submergence of the valley slopes1 eroded before the rise of the water to its present height4 ,even the vertical photograph1 which does not register relative elevations1 shows a distinct difference between the shore line of this type of body of water and rivers with broad1 low flood plains4 ,the large trees close to the margin of the river and the cultivated fields just back of them indicate a relatively high bank4 ,scale1 about #a3i1jjj4 times he can see with great distinctness4 ,in trying to ascertain the most favorable conditions for such observation1 it was found that submerged objects are seen best when the sky is evenly overcast or when it is uniformly clear4 ,sometimes when the sky is only partly cloudy the surface of the water seems to act as a mirror and nothing is seen but the reflection of cloud and sky4 ,waves have less effect on the visibility of objects beneath the surface than was expected1 although they diffuse the reflected light to some extent and consequently weaken the image on the negative4 ,but the reflected light from the surface of the water is stronger than that coming from objects under water4 ,hence1 to photograph underwater features successfully1 a time should be chosen when direct reflection of light from the sun or from a brightly illuminated cloud will not enter the lens4 ,experience in both the air and the laboratory shows that the best results are likely to be obtained when the sunlight strikes the surface at an oblique angle4 ,in summer favorable times are mid-forenoon or mid-afternoon under an evenly illuminated sky4 ,in winter the sun is low enough at midday to avoid direct reflection into the lens4 ,but experience also indicates that often photographs taken at moments when the eye caught the image of a submerged object show only the surface of the water4 ,,chapter ,,ix ,,the ,,plain ,,from ,,the ,,air 7,,figs4 #cd ,,to #da7 ,a ,,river ,,on ,,the ,,great ,,plains ,the difficulty of photographing a plain from a point on its surface needs no emphasis1 but its successful representation by means of air photographs is illustrated by many figures in this book4 ,the ,great ,plains of the west-central part of the ,united ,states are illustrated here by a view of the ,red ,river 7,fig4 #cf71 which shows the flat surface of the land and the broad sandy bed of the river only partly covered by the intricately woven strands of the braided channels--a scene characteristic of the ,great ,plains4 ,,meandering ,,streams ,,on ,,the ,,coastal ,,plain ,the ox-bow curves of meandering streams are among the features of the earth's surface most familiar to the student of physical geography2 yet1 heretofore1 they have been illustrated only by maps1 constructed at great labor and expense4 ,comprehensive photographs of them are rare and are1 at best1 imperfect and unsatisfactory for purposes of illustration4 ,on the other hand1 meandering streams lend themselves admirably to air photography4 ,equally familiar to the student of geography and physiography is the term 8abandoned meander40 ,these ancient stream courses1 many of which are now occupied by marsh1 brush1 or forest1 have been still more difficult to illustrate by means of photographs4 ,in some instances wooded meanders like those near ,columbus1 ,ga4 7,fig4 #cd71 long ago abandoned by the stream that formed them1 are shown in air pictures in a manner but little less conspicuous than the meanders of the present-day stream4 ,it is believed that instructors will find ,figure #cd useful1 not only in illustrating meandering streams and abandoned meanders but also in showing how meanders develop4 ,illustration3 ,,fig4 #cd ,illustration3 ,,fig4 #ce ,illustration3 ,,fig4 #cd--,the ,chattahoochee ,river south of ,columbus1 ,ga41 showing the results of progressive lateral shifting of a meandering stream4 ,in the upper part of the illustration to the left 7west7 of the stream are light-colored concentric markings which probably represent the gradual shifting of the stream toward the right4 ,as interpreted from the information at hand1 this section of the stream at one time occupied a position much farther west than now4 ,it cut away the bank on the east1 forming a curved course1 depositing sand and mud on the inside of the curve4 ,this typical feature of stream erosion and deposition is to be noted from the picture of the present course of the stream4 ,at the outside of each meander stretches of the bank appear light-colored and denuded of the trees and bushes that line the bank elsewhere4 ,these are scours1 a slipping away of the bluff caused by the cutting of the stream into the foot of the bank at points where the velocity of the outside of the current1 and consequently its corrosive power1 is increased as it swings round the curve4 ,the inside of the sharpest meander shows also the deposit of material due to the fact that the velocity of the inside of the current is checked by the bank1 causing it to deposit some of its load4 ,added to this deposit is much of the material brought by cross-currents from the opposite-lying scour4 ,the light-colored banks are probably successive deposits4 ,finally1 either by a gradual wearing away or by some whim of the current at flood tide1 the river chose a shorter course1 leaving its old channel as an abandoned meander4 ,farther south several abandoned meanders may be distinguished1 each distinctively marked by a steep bank on the outside of the curve and concentric bandings on the inside4 ,the abandoned channels are especially marked by the trees and brush that fill them in many places4 ,it appears that a well-developed growth of trees is to be found only along the river banks in this region and the growth in the abandoned channels is probably due to the fact that in flood time there is much seepage of water into these old channels if not an actual overflow from the present course of the stream4 ,at the bottom of the picture is to be seen the recently made land under cultivation4 ,the fields appear striated and checkered1 obscuring the concentric banding4 ,the illustration is from a mosaic made up at ,camp ,benning near-by of many photographs matched together1 hence there are certain differences in shade due to dark and light prints4 ,scale1 about #a3ch1jjj4 ,illustration3 ,,fig4 #ce--,map of the same area shown in ,fig4 #cd enlarged from the corresponding sections of the ,columbus and ,seale1 ,ga4-,ala41 topographic sheets1 #a3fb1ejj1 published by the ,u4 ,s4 ,geological ,survey4 ,the cross section at the bottom lies along the line indicated on the map and extends somewhat beyond the right border of the map4 ,the section shows between the hills the broad lowland over which the ,chattahoochee ,river has meandered4 ,scale1 #a3ch1jjj4 ,illustration3 ,,fig4 #cf--;,a river channel in the ,great ,plains4 ,the ,red ,river northeast of ,wichita ,falls1 ,tex41 as photographed from a height of #h1jjj feet1 ,september #ab1 #aiah4 ,between the bluffs is seen the dark-colored water of the braided stream flowing on a broad sandy bed more than a mile wide1 which is completely covered with water only at flood time4 ,the river forms the ,texas-,oklahoma boundary1 and frequent changes in the position of the channel during periods of high water make the exact position of the interstate boundary uncertain and give rise to disputes and litigation over the ownership of land4 ,north of the river 7top of figure7 to the right are sand dunes with a sprinkling of trees and bushes2 in the middle of the channel there is an island of light-colored sand4 ,the stream channel bites sharply into the southern bluff1 which is cut by many strong gulches4 ,across the river is the familiar sand flat built of the material washed downstream at flood time and spread out by the subsiding water4 ,the channel at this point shows the changes that have taken place in the position of the stream and1 where the stream crosses the sandy floor1 affords an example of braiding4 ,scale1 about #a3bc1jjj4 ,illustration3 ,,fig4 #cg--;,a characteristic glacial drift plain in southwestern ,michigan4 ,there appear1 at the left1 the round surface of a terminal moraine and gullied slopes1 which show mottled in the picture2 morainic hollows and kettleholes once partly filled with water but now filled with peat or occupied by marshes formed by the accumulation of peat from plant growth until carbonaceous matter has replaced the water of the original lake2 in the center1 a relatively smooth outwash plain characterized by straight roads and well-cultivated fields2 and1 at the right1 a brush-lined creek1 a small reservoir1 and the town of ,flowerfield4 ,scale1 about #a3bj1jjj4 ,illustration3 ,,fig4 #ch--,the same area as shown in ,fig4 #cg1 enlarged from the advance edition1 #a3dh1jjj1 of the ,schoolcraft1 ,mich41 topographic sheet to be published by the ,u4 ,s4 ,geological ,survey4 ,this advance sheet results from an experiment in the use of airplanes for mapping4 ,the area was photographed with a mapping camera4 ,from the photograph a base map was constructed1 which was verified on the ground2 on this base the contour lines were added by instrumental survey4 ,scale1 #a3bj1jjj4 ,illustration3 ,,fig4 #ci--,schoolcraft1 ,mich41 a town typical of the agricultural portions of the north-central ,united ,states1 showing the characteristic features--roads1 fields1 town blocks1 and others--by which the aviator can recognize a locality from a distance4 ,the mottled appearance of the land surrounding the village is characteristic of air photographs of glacial moraine regions4 ,the picture of the village itself might be taken as a prototype of the ,american village with its fairly regular layout of streets1 its business center indicated by a few larger roofs along the widest street1 its lawns1 trees1 and gardens1 the bordering farm lands1 and the scattered extensions of the village into points in the direction of the main roads4 ,scale1 about #a3ad1jjj4 ,,the ,,glacial ,,drift ,,plain ,illustration3 ,,fig4 #dj--,map of the town of ,schoolcraft1 ,mich41 for comparison with ,fig4 #ci4 ,enlarged from the advance edition1 #a3dh1jjj1 of the ,schoolcraft1 ,mich41 topographic sheet to be published by the ,u4 ,s4 ,geological ,survey4 ,scale1 #a3ad1jjj4 ,some of the characteristics of a third type of plain1 the glacial drift plain1 are shown in ,figures #cg to #da4 ,here are pictured glacial lakes1 bogs1 marshes1 moraines1 and outwash plains1 peat-filled depressions1 kettleholes and gullied slopes--typical features of a glaciated region4 ,the views show1 also1 many of the familiar aspects of the central and western parts of the ,united ,states3 the rectangular pattern formed by the land subdivisions established by the ,united ,states ,land ,office1 the checkerboard pattern being emphasized by the section-line roads2 the minor subdivisions into fields2 and the cultivation of a variety of crops4 ,illustration3 ,,fig4 #da--,kettleholes and other depressions in glacial till1 on the ,grand ,trunk ,railway about #e miles southwest of ,schoolcraft1 ,mich4 ,the distance between the eastern 7right7 edge of this view and the western 7left7 of ,fig4 #cg is about #a mile4 ,scale1 about #a3ae1jjj4 ,these photographs were selected from a series taken as an experiment in map-making4 ,in ,june1 #aibj1 the ,united ,states ,air ,service sent a plane equipped with a ,k-#a camera from ,dayton1 ,ohio1 to ,schoolcraft1 ,mich1 where in seven hours' flying time a fifteen-minute quadrangle1 about #bbj square miles1 was photographed4 ,the prints were matched together and reduced to a scale of #a3dh1jjj4 ,from them such features as roads1 streams1 forests1 land corners1 etc41 were transferred to plane-table sheets1 which the topographic engineers on the ground then used for contouring the relief4 ,figure #ch is a part of the preliminary proof of this map4 ,it may be added that the experiment is regarded as highly favorable to the use of the airplane camera as an instrument in mapping4 ,,chapter ,x ,,mountain ,,features 7,,figs4 #db ,,to #eb7 ,in obtaining photographic illustrations from the ground of mountains1 canyons1 and associated land forms1 the same difficulty1 but in exaggerated form1 is encountered that obtains in securing an advantageous point of view for small objects4 ,the difficulty is overcome in large measure by the use of aircraft4 ,in an airplane the observer can rise above the obstructions which interfere with the view desired2 can look an isolated mountain peak squarely in the face1 as in the case of the photograph of ,mt4 ,shasta 7,fig4 #db72 can study the details of its ice cap 7,fig4 #db7 and gaze downward on the lateral and recessional moraines left by the retreat of the mountain's glaciers 7,fig4 #dc74 ,few volcanic craters1 occurring as they do at the top of cones1 have been successfully photographed unless some higher mountain stands near-by on which a favorable viewpoint can be found4 ,from an airplane1 however1 one can look into the very throat of a crater1 as into that of ,cinder ,cone 7,fig4 #dh71 near ,lassen ,peak1 ,california4 ,much attention has been given to the interrelations of canyons1 gorges1 and mountain ridges1 but these relations have hitherto been illustrated chiefly by means of maps and charts4 ,figures #di1 #ej1 and #eb picture three relations more expressively than any map4 ,to the experienced geographer a map may illustrate perfectly the action of a stream working headward into higher land2 but the student to whom the conception of headward erosion is new will certainly grasp the idea more readily from the picture presented in ,figure #eb4 ,no map could give so clear a conception of a maturely dissected highland as does a photograph like that of the ,santa ,monica ,mountains 7,fig4 #ej74 ,illustration3 ,,fig4 #db--;,a glaciated volcanic ,cone3 ,mt4 ,shasta1 ,california1 #ad1afb feet high1 as seen by an airplane observer from the northeast1 showing ,hotlum ,glacier in the foreground and ,wintun ,glacier at the extreme left4 ,the monadnock which separates the two main lobes of ,hotlum ,glacier appears as the dark-colored mass of rock in the midst of the ice4 ,to be noted are the many indications of movement in the glaciers shown by curved lines1 eddies1 and crevasses1 and the glacial streams flowing away from the ends of the glaciers4 ,the long lobe at the left center shows the formation of both lateral and recessional as well as terminal moraines4 ,illustration3 ,,fig4 #dc--;,a glacial gorge on the northeastern face of ,mt4 ,shasta1 ,california1 below ,hotlum ,glacier 7see ,fig4 #db71 the lower end of which is to be seen in the upper part of the photograph4 ,at the left are two ridges1 one the edge of a sheet of flow lava1 the other1 in part at least1 a lateral moraine4 ,in the center1 at the bottom of the gorge1 between the two white lines which represent glacial streams1 is a system of concentric ridges which are probably recessional moraines4 ,at the right is the western slope of the gorge4 7,this figure is the lower overlapping continuation of ,fig4 #db47 ,illustration3 ,,fig4 #dd--,yosemite ,valley1 ,california1 a typical ice-shaped gorge1 showing at the left the granite face of ,el ,capitan1 about #c1jjj feet above the bottom of the famous gorge1 and1 at the right1 the pinnacle of ,sentinel ,rock and the well-known form of ,half ,dome4 ,at the sky line in the center of the picture is ,clouds ,rest1 and well down in the gorge ,washington ,column and the ,royal ,arches can be distinguished4 ,these photographs have the advantage of appealing to the mind through the sense of vision and will serve the same purpose as plaster models4 ,thus1 in ,figure #eb1 a variety of topographic forms are to be distinguished1 including slightly dissected highlands with sharply incised gorges2 maturely dissected highlands made up now of canyons and ridges2 a mountain valley broadening out toward an intermontane plain2 several arroyos2 and many minor features4 ,in the interpretation of the features shown in a vertical view of a mountainous country the orientation of the photograph is of prime importance4 ,when viewed in proper orientation1 that is1 as already pointed out 7p4 #e71 with the shadows falling toward the observer1 mountains and valleys appear in their correct relation4 ,but1 if the position of the picture is reversed1 a mountain will look like a depression and a valley like a ridge4 ,this reversal of the image can be tested by looking at ,figures #di or #eb from both viewpoints4 ,however1 since the vertical photographs will be compared with maps of the same area1 it is thought better to place them on the page as if they were maps4 ,in order to make them appear natural the prints can be turned in the necessary direction4 ,illustration3 ,,fig4 #de--,map of the ,yosemite ,valley1 showing the area included within the angle of vision of ,fig4 #dd4 ,the map1 a reduced section from the ,yosemite and ,mt4 ,lyell1 ,cal41 topographic sheets1 #a3abe1jjj1 published by the ,u4 ,s4 ,geological ,survey1 is oriented for direct comparison with the photograph4 ,scale1 #a3afg1jjj4 ,illustration3 ,,fig4 #df--,mountains of volcanic origin3 ,cinder ,cone with1 in the distance at the right1 ,lassen ,peak in the northern ,sierra ,nevada1 ,california1 as seen from an airplane over ,lake ,bidwell4 ,beyond the lake appears the rough surface of lava poured out as molten rock less than two hundred years ago 7see ,u4 ,s4 ,geol4 ,survey ,bull4 #gi1 #ahia74 ,surrounding the cone is a light-colored ash field1 sparsely forested at the right1 which was formed about two hundred years ago4 ,the mountain in the middle of the photograph having a smooth surface is ,cinder ,cone1 rising #fdj feet above the general level of the ash field and consisting of fragments of lava--the so-called ash and cinders--blown from the crater at times of eruption4 ,illustration3 ,,fig4 #dg--,map of the region between ,cinder ,cone and ,lassen ,peak in the northern ,sierra ,nevada1 ,california1 showing the area included within the angle of vision of ,fig4 #df4 ,the map1 a reduced section from the ,lassen ,peak1 ,cal41 topographic sheet1 #a3bej1jjj1 published by the ,u4 ,s4 ,geological ,survey1 is oriented for direct comparison with the photograph4 ,scale1 #a3cjg1jjj4 ,illustration3 ,,fig4 #dh--,the top of ,cinder ,cone1 looking from an airplane down into the crater1 showing a large saucer-shaped crater #gej feet across1 with a deeper crater formed at the time of a later volcanic explosion1 which looks like a cup in the middle of the saucer and extends to a depth of #bdj feet below the outer rim4 ,on the barren cinder slopes at the right is the pathway by which the crater can be reached4 ,illustration3 ,,fig4 #di--,mountain1 valley1 and plain in the ,simi ,hills about #ae miles northwest of ,santa ,monica1 ,cal4 7see ,calabasas1 ,cal41 topographic sheet71 showing1 in the right center of the picture1 headward erosion from two parallel valleys1 in strong contrast with the gently rounded1 slightly dissected part of the mountain 7left center7 into which the streams have not yet eaten their way4 ,farther up the mountain is more maturely dissected and the divides are narrow and steep4 ,on its top the mountain shows little effect of stream erosion 7right74 ,strongly cut gorges and arroyos appear where the streams enter the plain 7left74 ,probably north is at the bottom of the photograph4 ,scale1 probably about #a3bj1jjj4 ,illustration3 ,,fig4 #ej--;,a maturely dissected highland3 ,santa ,monica ,mountains north of ,santa ,monica1 ,cal41 as photographed from a height of nearly #aj1jjj feet at a midday in ,january1 #aiai4 ,the light-colored irregular line at the left is ,sepulveda ,canyon2 and the similar line at the right1 ,stone ,canyon 7for location1 see ,fig4 #ea74 ,these mountains rise nearly #a1fjj feet above sea level and about #gjj feet above the bottom of the canyons4 ,to obtain the proper impression of ridges and valleys the figure should be reversed4 ,such photographs as this of the actual ground can hardly be distinguished from photographs of good relief models2 they strikingly confirm the correctness of this and similar methods of representing relief on maps1 developed intuitively1 as it were1 such as the ,swiss school of hill shading4 ,scale1 about #a3ag1jjj4 ,illustration3 ,,fig4 #ea--,map of the region between the center of ,los ,angeles and ,santa ,monica1 ,cal41 showing the location of the area covered in ,fig4 #ej 7the double-ruled rectangle in the upper left corner74 ,reduced from the ,santa ,monica1 ,cal41 sheet1 #a3fb1ejj1 of the 8,progressive ,military ,map0 of the ,united ,states being published by the ,corps of ,engineers1 ,u4,s4,a4 ,this sheet1 which is the equivalent of the ,santa ,monica topographic sheet surveyed in #ahic and published by the ,u4,s4 ,geological ,survey1 was revised in #aibj by airplane photography4 ,a comparison of the #ahic and #aibj editions brings out strikingly the rapid urban development in this region4 ,scale1 #a3abc1jjj4 ,illustration3 ,,fig4 #eb--;,a young mountain gorge showing an erosional hollow developing headward into the less deeply eroded highlands3 ,san ,joaquin ,hills1 a coastal range in ,southern ,california about #de miles southeast of ,los ,angeles1 near the mouth of ,aliso ,creek4 ,north is at the left 7see ,corona1 ,cal41 topographic sheet74 ,scale1 probably about #a3aj1jjj4 ,,chapter ,,xi ,,air ,,craft ,,in ,,the ,,study ,,of ,,rocks ,,and ,,ores 7,,fig4 #ec7 ,the admirable manner in which air photography lends itself to the observation of geographic relations and physiographic processes suggests its use as a valuable addition to the instruments of geologic reconnaissance2 for1 not only is the study of geology inseparable from that of physiography1 but1 in large measure1 geology is applied physical geography and many conclusions of a geologic nature are drawn from observed surface relations4 ,probably1 in most cases1 the actual character and composition of rocks cannot be determined from air photographs2 but1 just as on a good map an area of crystalline rocks can be distinguished from one of sedimentary rocks by means of the topographic expression1 so areas of different rocks can be distinguished on photographs4 ,for instance1 an area of upturned sedimentary rocks would be readily distinguished from one of horizontal rocks4 ,figure #db shows how the character of glaciated mountains is revealed1 and ,figures #cg to #da of the ,michigan area show well the familiar features of continental glaciation4 ,it is perhaps premature to say much of the use of the airplane in the study of geology until it has been thoroughly tested4 ,but it should be possible from the air to locate and map ore bodies1 metalliferous veins1 and outcrops of rock3 for it is well known that rocks at the outcrop differ in color1 in the forms of erosion developed in them1 and in the kind of plants which they support4 ,it is of interest that ,colonel ,alfred ,h4 ,brooks1 who was ,chief ,geologist of the ,american ,expeditionary ,forces in ,france during the war1 found that geologic boundaries could be recognized on air photographs and that by means of these photographs he could correct existing geologic maps and identify ,illustration3 ,,fig4 #ec--;,canyon in sedimentary rocks near the mouth of the ,pecos ,river1 ,texas4 ,the rocks consist of flat-lying strata1 and the tortuous lines resembling the grain in wood denote the outcrops of hard layers and the benches formed on these layers by erosion4 ,this photograph illustrates the use of air photography in geological reconnaissance4 ,scale not known4 formations in inaccessible areas within the enemy lines4 ,his method was to use air photographs in the study of the geologic formations of areas accessible to him4 ,then1 having familiarized himself with the appearance of the different rock formations and structures on the photographs1 he was able to recognize the same features on photographs of areas held by the enemy and so project his mapping over into inaccessible territory4#d ,the prospector should effect a great saving of time by using air photographs to guide him to places where he can find exposures of rock and to help him to avoid places where it would be useless to look for exposures4 ,particularly in wooded regions air photographs are valuable in indicating localities where exposures can be found in areas so covered with forest that examination on the ground would not be worthy of consideration4 ,prospectors for oil are planning to use airplanes for this purpose in northern ,canada1 in ,south ,america1 and in other places where much of the country is so densely wooded that much time is usually spent in looking for clear space4 ,,use ,,in ,,exploration ,exploratory work should benefit in many ways4 ,general reconnaissance has been carried on to a considerable extent in foreign lands with airplanes and to some extent also in ,america4 ,wide areas along the ,mexican border have been photographed for the making of new maps and for the correction of existing maps4 ,the same photographs would be useful in geologic reconnaissance4 ,the new photographs of southern ,arizona are said to show mountain ranges many miles away from their location on existing maps4 ,such corrections are of importance to the geologist as well as to the geographer and the map-maker4 ,amundsen intends to employ several small planes in his ,arctic work now under way4 ,mjberg#e has projected an expedition to ,new ,guinea in which the use of airplanes is a fundamental condition4 ,,chapter ,,xii ,,mapping ,,and ,,charting ,,from ,,the ,,air 7,,figs4 #ed ,,to #hb7 ,mention has already been made 7p4 #ef7 of the experiment in map-making carried out by the ,army ,air ,service and the ,united ,states ,geological ,survey at ,schoolcraft1 ,mich4 ,the results of that experiment and of others of the sort are sufficient to establish the fact that the air camera is destined to become a valuable addition to the map-maker's equipment4 ,the extent to which it will be used depends1 of course1 upon the degree to which its present imperfections are corrected and its possibilities developed4 ,the ,board of ,surveys and ,maps of the ,united ,states government has recently published the results of its study of air photography for use in map-making4#f ,illustration3 ,,fig4 #ed--,view across the western end of ,lake ,erie1 looking in a northeasterly direction 7see ,fig4 #ee74 ,oblique photograph taken from #ah1jjj feet above ,port ,clinton1 ,ohio1 by ,lieut4 ,g4 ,w4 ,goddard1 showing1 in the foreground at the right1 ,catawba 8,island10 a part of the mainland1 and1 at the left1 ,put-in-,bay and the islands around it4 ,in the distance below the white clouds are a small island 7,middle ,island7 and a large one 7,pelee ,island74 ,in the upper left-hand corner is seen ,point ,pelee and the ,canadian shore to the northeast of it about #cj miles away4 ,at ,put-in-,bay was fought1 ,september #aj1 #ahac1 the ,battle of ,lake ,erie1 in which ,commodore ,perry defeated the ,british4 ,the monument commemorating this victory can be distinguished in the photograph as a white shaft4 ,although most vertical airplane photographs are in the nature of large-scale maps1 this view illustrates how a large area can be covered in an oblique view taken at a high altitude--an area1 when transformed1 of appreciable size even on a small-scale map1 such as1 for example1 ,fig4 #ee4 ,illustration3 ,,fig4 #ee--,map of the western end of ,lake ,erie showing the area covered within the angle of vision of ,fig4 #ed4 ,scale1 #a3a1djj1jjj4 ,,figs4 #ed 7upper7 and #ee 7lower74 ,for explanation1 see bottom of opposite page4 ,,scale ,,and ,,horizontal ,,control ,,of ,,vertical ,,photographs ,the vertical photographs taken with an air camera are1 of course1 of the order of large-scale maps4#g ,for a lens of #f-;inch focus the scale at an elevation of #b1ejj feet will be #a3e1jjj2 at #e1jjj feet1 #a3aj1jjj2 and at #aj1jjj feet1 #a3bj1jjj4h ,air mapping1 therefore1 lends itself best to the production of such maps as engineering maps1 city plans1 topographic maps1 and coast charts4 ,in all of these maps a degree of accuracy is demanded that will give the exact location of all the features included on the map and permit the precise measurement of distances between them4 ,to obtain such accuracy necessitates an elaborate system of control stations as a basis on which the surveyor works out his triangulations and traverses4 ,in the ,united ,states these controls have been established principally by the ,united ,states ,coast and ,geodetic ,survey4#i ,to construct a map from air photographs1 varying in scale and distorted as they often are because of the impossibility of holding the plane at an absolute level and because of the stretching or shrinkage of the photographic paper1 would require a great amount of triangulation and traverse in order that the control might be sufficiently detailed to permit the accurate mounting of the photographic prints4 ,but1 given these controls1 the air camera can1 without further adaptation1 supply details that heretofore required the laborious processes of plane-table mapping4 ,the topographer can place the two-dimensional details from photographs and then go into the field with only the contouring to be done4 ,illustration3 ,,fig4 #ef ,illustration3 ,,fig4 #eg ,illustration3 ,,fig4 #eh--;,index map showing the location of the areas shown on airplane photographs in this book within the ,atlantic seaboard of the northeastern ,united ,states1 except those whose exact location is unknown 7,figs4 #ba1 #bc1 #bh1 #bi1 and #gg74 ,scale1 #a3b1hjj1jjj4 ,illustration3 ,,fig4 #ei--;,an area where charting of the coast line is difficult3 ,marshlands on ,chesapeake ,bay which are exposed at low tide and submerged at high tide4 ,location3 ,south of the mouth of the ,york ,river1 ,virginia1 between the estuaries of ,poquoson ,river and ,back ,river4 ,scale1 about #a3b1ejj4 ,illustration3 ,,fig4 #fj--;,beach and bluff3 ,left shore of the ,york ,river north-northwest of ,gloucester ,point1 ,va41 showing a tied island 7one of the ,mumfort ,islands7 and a narrow band of beach between the water and the bluff1 which is #bj to #ej feet above the water4 ,the plain back of the bluff is recognized by the checkered pattern made by the cultivated fields4 ,scale1 about #a3i1jjj4 ,illustration3 ,,fig4 #fa--;,a sandy beach with beach cusps forming the extreme northwestern end of ,sandy ,hook1 ,new ,jersey1 showing1 at the left1 the end of the ,hook surrounded by light-colored sand shading off to shoals and bars2 at the right1 a broad belt of sand where a new point is beginning to form2 and1 between them1 six cusps arranged like saw teeth4 ,note that a wave breaks into foam at the point of each cusp4 ,scale1 about #a3i1jjj4 ,,use ,,in ,,city ,,mapping ,in city mapping1 even though time be taken to establish a very elaborate system of controls1 the air camera can accomplish in a few hours a task of years by ordinary methods4 ,in fact it is only by means of air photographs that maps of a growing city can be kept at all up to date4 ,paris was mapped with #hjj plates in less than one day of actual flying4 ,washington was completely mapped in two and a half hours with less than #bjj exposures4#aj ,for the mosaic of ,rochester1 ,n4 ,y4 7,fig4 #ef7 #hb photographs were made in one hour and twenty minutes4 ,there is no reason why such a mosaic with an original survey or even a number of accurately located points as a basis of control should not be sufficiently accurate for all purposes4 ,,use ,,in ,,revision ,,of ,,existing ,,maps ,another immediate use of air photographs in mapping is in the correction and revision of existing maps4 ,so far as individual features are concerned1 the air photograph is an exact record of the area exposed to its lens1 and natural and artificial features are easily transferred from the picture to the map4 ,its great value in the saving of time and money has been demonstrated in the rapidly developing territory near ,los ,angeles4 ,in #ahic the ,santa ,monica quadrangle was surveyed1 and houses1 roads1 etc41 as they existed at that time1 are shown on the map4 ,this area was later built up and so changed that the map was practically worthless4 ,from information derived from air photographs the map was revised in #aibj 7,fig4 #ea74 ,evidence has already been given of the efficiency of the air photograph in elaborating maps where the importance of the region is not sufficient to warrant the expense of a detailed survey of minor features1 and in mapping areas inaccessible from the ground4 ,illustration3 ,,fig4 #fb--;,beach cusps extended under water and showing the interference of waves off the curved beach on the bay side north of ,beach ,haven1 ,n4 ,j4 ,scale1 about #a3c1jjj4 ,illustration3 ,,fig4 #fc--;,first stage in the formation of an inlet through a barrier beach1 where ocean waves during some storm1 probably at high tide1 broke over the sand barrier #b miles north of ,beach ,haven1 ,n4 ,j41 and washed some of its sand into ,little ,egg ,harbor4 7,for another good example of wash-overs1 see ,fig4 #fh47 ,scale1 about #a3i1jjj4 ,illustration3 ,,fig4 #fd--;,a tidal delta in ,shark ,river ,inlet1 ,belmar1 ,n4 ,j41 as photographed from a height of #aj1jjj feet1 showing shoals at the left1 which appear shadowy because they are under water1 and the small channels which radiate outward from the narrow inlet like the ribs of a fan4 ,they are the distributaries of this underwater delta4 ,scale1 about #a3aa1jjj4 ,,use ,,in ,,coast ,,charting ,illustration3 ,,fig4 #fe--;,a tidal delta built up until it is partly above water3 ,popes ,creek1 ,virginia1 on the right bank of the lower ,potomac ,river1 #d miles southeast of ,colonial ,beach1 as seen obliquely from a height of #d1jjj feet at #c3cj ,p4,m41 ,august #ca1 #aibj4 ,the tidal currents from the ,potomac have built hook-shaped bars nearly across the outlet of the creek1 and the inflowing currents have built a delta from the mouth of the creek upstream4 ,it is fortunate for those engaged in the study of shore features and the mapping of coasts that1 being flat1 shore features are particularly well adapted to representation by air photographs1 for on coasts exposed to the wind and waves the channels1 shoals and bars are continually changing4 ,air photography offers a quick and convenient means of keeping charts up to date4 ,the intricacies of the water line in some places makes accurate charting by the ordinary survey methods a slow1 laborious process4 ,when bluffs or relatively steep slopes1 like those of ,york ,river1 ,virginia1 near ,gloucester ,point1 shown in ,figure #fj1 ,illustration3 ,,fig4 #ff4 7,for explanation1 see next page47 ,illustration3 ,,fig4 #ff--;,a double tidal delta at ,barnegat ,inlet1 ,new ,jersey1 as photographed from a height of #aj1jjj feet4 ,to the east 7right7 the breaking waves and shadowy depths indicate the position of shoals4 ,west of the surf belt are the light-colored beach sand1 shading off from the conspicuous hook at the southern end of ,island ,beach into underwater shoals and bars1 and older surfaces made dark-colored by the growth of plants4 ,south of the hook are the inlet leading into ,barnegat ,bay and the northern end of ,long ,beach1 at the point of which stands a lighthouse whose long shadow is to be seen across the beach sand4 ,the mottled appearance of the bay to the left is due to shoals slightly submerged or perhaps exposed at low tide1 where dark-colored drainage lines appear1 and shading off to deeper water1 where the submerged land forms have a shadowy appearance4 ,the distribution of the shoals indicates that this is a double tidal delta1 an infacing part west of the inlet and an ocean-facing part to the right4 ,scale1 about #a3ag1jjj4 ,illustration3 ,,fig4 #fg ,,fig4 #fg--;,a tidal inlet through the barrier beach south of ,beach ,haven1 ,n4 ,j41 connecting the ,atlantic ,ocean to the right 7east7 with ,little ,egg ,harbor to the left4 ,the beach sand south of the inlet is little above water level and is frequently washed by waves1 which shift the sand and produce the clouded appearance of the sandy surface4 ,the light-colored ragged belt at the right is surf2 the continuous narrow belt1 beach sand2 the clouded areas1 recently washed wet or slightly submerged sand4 7,the ordinary tidal variation here is #d4b feet47 ,this inlet does not appear on the #aiad edition of ,u4 ,s4 ,coast and ,geodetic ,survey ,chart #abaf1 and sand hooks had little more than begun to form then4 ,scale1 about #a3ad1jjj4 ,illustration3 ,,fig4 #fh4 7,for explanation see bottom of next page47 ,illustration3 ,,fig4 #fh--;,beach between ,brigantine and ,little ,egg ,inlets1 ,new ,jersey1 showing a variety of features characteristic of a wave-built sand barrier4 ,the upper 7northern7 part of the illustration shows several places where waves have broken over the sand barrier and washed the sand westward1 where it was redeposited at the left in the quiet1 protected water4 ,farther south are older wash-overs1 where the enclosed bay is nearly filled with sand4 ,at the left are numerous islands1 streams1 and flats characteristic of the salt marshes west of the barrier beach along the ,new ,jersey coast4 ,scale1 about #a3g1jjj4 ,illustration3 ,,fig4 #fi--;,a simple spit3 ,lower ,cedar ,point1 ,maryland1 on the left bank of the lower ,potomac ,river1 #f miles north of ,colonial ,beach1 ,va41 as seen obliquely downward from a height of #d1jjj feet4 ,the white line on either side of the point is sand at the foot of bluffs4 ,houses and fields are seen at the left4 occur along the shore1 the water line varies little from year to year4 ,but on very low lands1 like those along ,chesapeake ,bay south of the mouth of ,york ,river1 shown in ,figure #ei1 the strand may migrate over a broad belt between high and low tide4 ,for this reason it is desirable that photographs of areas affected by the tide be accompanied by a record of the date and time of day at which the exposure was made1 in order that the height of the tide at the time of exposure can be computed4 ,as the shore on the ,coast and ,geodetic ,survey charts denotes the water line at high tide1 a photograph taken at low tide might be interpreted as indicating an error on the chart4 ,where the water migrates over such a broad belt of sand or mud1 the problems of charting become very troublesome4 ,photographs of such areas could be taken at both low and high tide1 and from these the belt of daily flooding could be charted4 ,illustration3 ,,fig4 #gj--;,a hook1 or recurved spit1 south of ,brigantine ,inlet1 ,new ,jersey1 as photographed from a height of #aj1jjj feet1 showing the strong curving upstream characteristic of spits on this ocean-facing coast4 ,the growing end of the spit1 resembling a lily bud1 shows an underwater extension beyond the light-colored beach sand4 ,to be noted is the filling in of the lagoon behind the reef and its pools and drainage lines4 ,this figure is practically a southern continuation of ,fig4 #fh4 ,scale1 about #a3i4jjj4 ,,experiments ,,by ,,the ,,united ,,states1 ,,french1 ,,and ,,other ,,coast ,,surveys ,the use of photographs in charting the coast line was tested by the ,united ,states ,coast and ,geodetic ,survey4#aa ,a flight was ,illustration3 ,,fig4 #ga--;,a hook1 or recurved spit1 showing interference with natural growth3 ,the northern end of ,ocean ,city4 ,n4 ,j41 as photographed from a height of #aj1jjj feet4 ,at the right 7east7 appears the curved body of sand1 light-colored where dried1 darker-colored where bathed by the waves and fringed by surf4 ,to the left certain 8improvements0 seem to have interfered with the natural growth of the spit1 and a small bay of shallow water has been enclosed by the formation of a bay-mouth bar across the outlet to the north4 ,scale1 about #a3ad1jjj4 made over the coast of ,new ,jersey by ,captain ,a4 ,w4 ,stevens of the ,united ,states ,army ,air ,service1 ,march #bj1 #aibj1 in a plane equipped with a ,k-#a camera of #aj-;inch focal length1 which makes negatives #ah by #bd centimeters in size4 ,during the flight the camera was maintained at an altitude of about #aj1jjj feet4 ,the course was covered by #ahc exposures made at such intervals of time that the prints overlap4 ,unfortunately the exposures were not sufficient to give all the details desired for marsh and water areas1 but prints were made on developing paper suitable for showing extreme contrast4 ,these were matched together and a continuous picture obtained4 ,a part ,illustration3 ,,fig4 #gb--,new ,point ,comfort1 a complex recurved spit at the tip of the peninsula enclosed by the ,york and ,rappahannock ,rivers1 ,virginia4 ,a vertical view taken from an altitude of about #aj1jjj feet1 showing in order from right to left 7east to west73 the wavy surface of ,chesapeake ,bay2 a light-colored band of beach sand curving westward in a compound hook made dark-colored in some places by trees and brush2 a shallow bay west of the beach in which may be seen shoals1 channels1 and sand bars under water2 and low-lying areas showing woodland and cultivated fields4 ,the photograph was taken at a time of day when reflected light from the partly enclosed body of water was dispersed1 allowing the submerged forms to appear4 ,scale1 about #a3ab1jjj4 ,illustration3 ,,fig4 #gc--,lines of growth in a sand spit3 ,tucker ,beach1 ,new ,jersey1 as photographed from a height of #aj1jjj feet1 showing the growth southward by successive ridges1 which probably began as sand bars1 grew to be barriers by wave action1 were heightened by wind-blown sand1 and finally were added to the main body of the spit by the final filling of the enclosed lagoons4 ,to the right 7east7 is the ,atlantic ,ocean1 showing waves and surf near the light-colored beach sand4 ,farther to the left are the ridges of sand made dark-colored by vegetation1 bordered by light-colored beach sand on ,little ,egg ,inlet1 which appears to the south and west4 ,scale1 about #a3ad1jjj4 of this picture1 greatly reduced1 is reproduced as ,figure #bb4 ,several characteristic shore and salt marsh features are illustrated by this series of photographs1 and these are reproduced in separate figures together with illustrations of special features in other places4 ,illustration3 ,,fig4 #gd--;,an island developing toward the stage of being tied to the mainland by a double tombolo1 or connecting bar3 ,napatree ,point1 as photographed from a height of about #aj1jjj feet1 connected to the east by ,napatree ,beach with the mainland at ,watch ,hill1 ,r4 ,i41 and approaching connection to the north with the mainland near ,stonington1 ,conn4 ,on the outer side of the tombolos underwater shoals and bars are seen dimly at the right 7south1 ,block ,island ,sound side7 and more clearly at the left 7west1 ,fishers ,island ,sound71 where the boat landing is situated at the edge of a submerged shelf4 ,the surf appears as a thin white line1 the beach sand as a narrow light-colored belt1 and the higher land as dark-colored areas on which houses and other structures stand4 ,scale1 about #a3bd1jjj4 ,the main features illustrated in detail1 all of which are continually liable to change1 making the keeping of a map of the area at all up to date impossible by ordinary means1 are as follows3 coast of low-lying mainland 7,fig4 #fj72 mud or peat-covered beach 7,fig4 #ei72 sandy beach 7,fig4 #fc72 barrier beach 7,fig4 #fg72 beach cusps 7,figs4 #fa and #fb72 recurved spits or sand hooks 7,fig4 #gj and others72 compound hook 7,fig4 #gb72 lines of growth in the development of hooks 7,figs4 #gc72 tombolos and tied islands 7,figs4 #fj and #gd74 ,illustration3 ,,fig4 #ge--,oblique view of the mouth of ,powells ,creek1 ,virginia1 on the right bank of the lower ,potomac ,river1 #e miles west of the ,naval ,proving ,grounds at ,indian ,head1 showing at the left the inner channel winding through the slightly submerged shoals and fading out toward the right where the channel crosses the submerged terrace of the ,potomac4 ,another experiment was made by the ,coast and ,geodetic ,survey off the coast of ,florida1 where the water is clear1 in an attempt to photograph 8the small coral heads and pinnacle rocks0 which may be disastrous to boats4 ,the report states that the results were unsatisfactory and concludes that airplane pictures are useful in 8aerial photo-topography0 but not in ,illustration3 ,,fig4 #gf--;,channels1 shoals1 and terraces in a drowned river valley3 ,roberts ,creek1 #i miles southeast of ,yorktown1 ,va41 an estuary tributary to ,chesapeake ,bay4 ,under the water in the drowned valley is seen the channel1 8braided0 in some places1 and extending out through sand bars to the deep water of ,poquoson ,river shown at the top 7north7 of the illustration4 ,at the left the dark-colored forest area is fringed with a narrow strip of white beach sand1 then with a belt of shallow water at the outer edge of which the waves form an irregular white line1 and beyond this with a belt which represents a submerged terrace4 ,scale1 about #a3ad1jjj4 ,illustration3 ,,fig4 #gg--,the underwater channel in ,quantico ,bay4 ,quantico ,creek is a tributary of the ,potomac ,river entering from the ,virginia side1 about #bh miles downstream from ,washington4 ,the 8,bay0 is the widened part of the stream at its entrance into the ,potomac1 which is entered by the tide4 ,forested land appears at the right and left1 with light-colored fields at the left4 ,the space between the wooded areas is occupied by shallow water1 beneath which appears the relatively deep channel1 which forks after the manner of streams4 ,the branching channel is wholly under water and differs in some respects from the channel of a normal stream4 ,among the more obvious peculiarities is the 8fanning out10 of the headwaters4 ,photograph taken from a height of about #ah1jjj feet4 ,scale1 about #a3ba1jjj4 ,illustration3 ,,fig4 #gh--,natural channels and shoals near ,miami1 ,fla43 an oblique view eastward to the ocean across ,bear's ,cut1 which is situated between ,biscayne ,key and ,virginia ,key4 ,because of the greater depth of water1 the channels with a maximum depth of #ag feet appear darker than the shoals4 ,the photograph was taken at a height of #c1jjj feet1 ,april #bj1 #aiah4 ,illustration3 ,,fig4 #gi--;,a dredged channel at ,miami1 ,fla43 an oblique photograph showing part of the city1 the boat landing1 the sandy beach1 and the shallow water1 through which a straight ship channel has been cut1 which appears dark-colored in the illustration because of the greater depth of water4 ,the photograph was taken ,april #bb1 #aiah1 from #ba height of #c1jjj feet4 ,illustration3 ,,fig4 #hj--;,a shoal in ,hereford ,inlet north of ,wildwood1 ,n4 ,j41 as seen from a height of #aj1jjj feet4 ,the breaking waves indicate that the shoal is only slightly submerged4 7,tidal variation is here about #d feet47 ,the sand spit north of the shoal1 the south end of ,sevenmile ,beach1 like other spits of the ,new ,jersey coast1 is building southward and may in time annex the shoal4 ,scale1 about #a3ac1jjj4 ,illustration3 ,,fig4 #ha--,sand bars at ,cape ,charles1 ,va4 ,south of the town at the right is the harbor1 into which a tug-boat is towing a barge4 ,west of the town 7left7 is a belt of light-colored beach sand and sand bars ending at the south against the breakwater1 north of the harbor4 ,the sand bars appear somewhat dim because they were photographed through water4 ,they are under water #a to #f feet deep at low tide1 or #d to #i feet at high tide4 ,scale1 about #a3f1jjj4 8aerial photo-hydrography40#ab ,on the other hand1 ,volmat reports the successful use of air photography for similar purposes on the ,french coast1 where photographs of objects down to a depth of #ag meters 7about #ef feet7 were found useful in several ways--among others1 the discovery of points of rock which had ,illustration3 ,,fig4 #hb--;,bars1 channels1 beaches1 and marsh near ,far ,rockaway1 ,long ,island1 ,n4 ,y41 as photographed from a height of #g1jjj feet at #aa ,a4,m41 ,september #ae1 #aibj4 ,in order from the bottom of the picture upward are3 ,east ,rockaway ,inlet with a shoal to the left and the sand hook at the end of ,long ,beach to the right of it2 the beach south of ,far ,rockaway with streets and houses2 a group of boats in the inlet at the right of the beach2 an area of salt marsh that is filling the lagoon behind the barrier beach2 and a small section of the village of ,far ,rockaway4 ,scale1 about #a3ab1jjj4 escaped attention during very detailed surveys4 ,he states that with proper plates and ray filters the presence of objects invisible to the eye is revealed by the camera4#ac ,similar use of air photographs has been made by the ,english in charting reefs1 shallows1 and harbors4 ,thomas says3 8,in #aiag aeroplane photography was successfully used for charting the harbor of ,rahbeg on the ,arabian coast40#ad ,it is a well-known fact that1 under proper conditions1 objects submerged to a considerable depth under clear water can be seen from points high above the surface4 ,during the war1 submarines were detected and followed by observers in airplanes1 and sunken vessels1 mines1 and other submerged objects have been located by observation from the air4 ,illustrations in this paper show the possibility of using this method of observation1 to some extent at least1 in detecting and mapping shoals1 channels1 and other features under water4 ,photographs of channels like those of the ,potomac ,river and its tributaries will be commercially as well as scientifically valuable4 ,the deep-water channel of the ,potomac is well known and has been charted2 but very little is known of many of the small tributary channels1 such as that of ,powells ,creek 7,fig4 #ge74 ,where the channels are not well known1 such a photograph could be used to advantage in avoiding the shoals1 and1 by surveyors1 first in exploratory work and later as a general guide in charting4 ,small boats entering this channel could use the photographs either for the original location of the deep channel in case no chart were available or for detecting changes in its course after the chart was made4 ,for uncharted channels1 like those of many of the tributaries of the ,potomac ,river1 air photography furnishes a quick and accurate means of location4 ,no amount of sounding1 charting1 or description could produce so accurate a mental picture of a drowned valley as that produced by ,figure #gf4 ,in ,figures #gh and #gi1 both of which were taken near ,miami1 ,florida1 is illustrated the difference in appearance between natural and artificial channels4 ,the straightaway course and regular outlines of the dredged channel contrast sharply with the winding course and merging outlines of the natural channel4 ,to the student of physiography and earth history the photographs furnish a means of observation of a definiteness heretofore quite unthought-of4 ,on them the actual shape of the channels1 submerged terraces1 and drowned land forms are shown in detail4 ,,improvements ,,under ,,way ,,point ,,to ,,promising ,,outlook ,,for ,,airplane ,,photography ,there is1 however1 need of careful research to determine the conditions under which the best results can be obtained4 ,the height and time of day for exposures with a certain lens1 the emulsion and kind of ray filter best suited under certain conditions1 the effect of light as it enters and emerges from the water1 and the effect of polarization are subjects demanding consideration4 ,chief among the experiments now under way is the determination of the kind of emulsion and ray filter or color screen that will give the best results4 ,it is a demonstrated fact that1 with an emulsion sensitive to red light1 objects in the air invisible to the eye because of intervening haze can be photographed through a red filter4 ,it is possible that water can be penetrated in the same way and that filters of other colors will prove advantageous4 ,certainly1 the air photograph is only in its infancy--but an infancy full of promise4 ,as a means of securing new and advantageous views of subjects of interest1 it is not only entertaining but scientifically and commercially valuable4 ,as an aid in mapping it can1 even in its present stage of development1 serve an important purpose by supplying accurate knowledge of otherwise inaccessible regions1 by furnishing details that are valuable but expensive to obtain1 and by permitting the frequent and inexpensive revision of existing maps4 ,,index ,accuracy1 #a1 #gd ,acknowledgments1 viii1 xi ,aerial photo-hydrography1 #ii ,aerial photo-topography1 #ic ,air photographs1 how to read1 #d2 improvements under way1 #ajb2 oblique and vertical1 #a2 value in coast charting1 #ic1 #ii1 #aja ,air photography1 application1 ix2 development1 ix2 elements to be recorded1 #b2 outlook1 #ajb ,air ,services1 co-operation1 xi ,aircraft1 x ,airplane photography4 ,see ,air photography ,aliso ,creek1 ,california1 #fh ,amundsen1 ,roald1 #ga ,anacostia flats1 ,d4 ,c41 #ab ,anacostia ,river1 #ac1 #bb 7ill472 land along1 mosaic photograph1 opp4 #cb 7,fig4 #ac7 ,animal trails1 #bi1 #ci ,annapolis1 #g4 ,see also ,united ,states ,naval ,academy ,arabian coast1 #aja ,architects1 #g1 #aa ,architecture1 #aa ,arizona1 southern1 #ga ,arroyos1 #fa1 #fe 7ill47 ,atlantic ,city1 ,n4 ,j41 #cb 7ill47 ,atlantic ,coastal ,plain1 #bg2 meandering streams1 #ej2 salt marsh areas1 #cb 7ill472 submarine land forms1 #de ,atlantic ,ocean1 waves and surf1 #ia 7ill47 ,back ,river1 ,virginia1 #gf ,bagley1 ,j4 ,w41 xii1 #gd ,baltimore and ,annapolis ,railroad bridge1 #i 7ill471 #aj ,barnegat ,bay1 #he ,barnegat ,inlet1 #hd 7ill471 #he ,barrier beaches1 #da2 between ,brigantine and ,little ,egg ,inlets1 ,new ,jersey1 #hf 7ill472 cities and surroundings1 #cb 7ill472 inlet formation through1 #ha 7ill472 ,long ,branch1 ,n4 ,j41 #ah 7ill472 tidal inlet through1 ,beach ,haven1 ,n4 ,j41 #he 7ill474 ,see also ,beaches ,beach ,haven1 ,n4 ,j41 cusps1 #hj 7ill472 inlet formation through barrier beach1 #ha 7ill472 tidal inlet1 #he 7ill47 ,beaches1 bluff and beach on shore of ,york ,river1 #gg 7ill472 cusps near ,beach ,haven1 #hj 7ill472 ,far ,rockaway1 ,long ,island1 #ajj 7ill472 sandy1 with cusps--,sandy ,hook1 #gh 7ill474 ,see also ,barrier beaches ,bear's ,cut1 ,florida coast1 #if 7ill47 ,belmar1 ,n4 ,j41 tidal delta1 #hb 7ill47 ,benning1 ,camp1 opp4 #bf1 opp4 #ej ,benning1 ,d4 ,c41 #ac1 #bb 7ill47 ,benning ,road1 #ac ,benning ,road ,bridge1 opp4 #bb 7ill4 and map7 ,bidwell1 ,lake1 ,california1 #fb 7ill471 #fc 7map7 ,bluffs1 #hc2 beach and bluff on shore of ,york ,river1 #gg 7ill47 ,board of ,surveys and ,maps1 #gb ,boundary disputes1 #bf2 ,texas-,oklahoma1 #ea 7ill47 ,braided channels1 #ej1 #ea 7ill47 ,brigantine ,inlet1 ,new ,jersey1 #hf 7ill471 #hg2 recurved spit1 #hh 7ill47 ,bridges1 #aa2 ,baltimore and ,annapolis ,railroad1 #i 7ill471 #aj2 ,benning ,road1 opp4 #bb 7ill4 and map72 ,hell ,gate1 #aa1 #ae 7ill472 ,pennsylvania ,avenue1 opp4 #bb 7ill4 and map7 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#h 7ill47 ,west ,point1 ,va41 #cf 7ill471 #ch2 marshes1 #bi1 #cj 7ill47 ,white ,house1 ,washington1 ,d4 ,c41 #af 7ill47 ,wichita ,falls1 ,tex41 #ea ,wildwood1 ,n4 ,j41 #ih ,wintun ,glacier1 #eh 7ill47 ,wright1 ,orville1 ix ,wright1 ,wilbur1 ix ,york ,river1 #ch1 #gf1 #hc1 #hg2 shoreline1 #gg 7ill47 ,yosemite and ,mt4 ,lyell topographic sheets1 #fa ,yosemite ,valley1 #fj 7ill471 #fa 7map7 ,,footnotes3 #a ,cf4 his ,the ,use of the ,panoramic ,camera in ,topographic ,surveying1 ,with ,notes on the ,application of ,photogrammetry to ,aerial ,surveys1 ,u4 ,s4 ,geol4 ,surrey ,bull4 #feg1 ,washington1 ,d4 ,c41 #aiag4 #b ,h4 ,e4 ,ives3 ,airplane ,photography1 ,philadelphia1 #aibj1 pp4 #cbh-cej4 #c ,the ,pamunkey gets its name from a tribe of ,indians famous in the early days of ,virginian history but now reduced to a few families living on a reservation situated on the banks of the river near ,lester ,manor4 ,mattaponi is a combination name4 ,the ,mat and the ,ta unite to form ,matta ,creek4 ,the ,matta and the ,po unite1 and ,ny ,creek is a tributary to the ,po4 ,the waters of these streams unite to form the river1 and the names ,mat1 ,ta1 ,po1 and ,ny unite to form its name--,mattaponi4 #d ,a4 ,h4 ,brooks1 personal communication4 #e ,eric ,mjberg3 ,a ,proposed ,arial ,expedition for the ,exploration of the ,unknown ,interior of ,new ,guinea1 ,geogr4 ,rev41 ,vol4 #c1 #aiag1 pp4 #hi-ajf4 #f ,the ,use of ,aerial ,photographs in ,topographic ,mapping3 ,a ,report of the ,committee on ,photographic ,surveying of the ,board of ,surveys and ,maps of the ,federal ,government1 #aibj1 ,air ,service ,information ,circular 7,aviation7 ,no4 #ahd1 ,war ,department1 ,washington1 ,d4 ,c41 #aiba4 #g ,what can be done1 however1 by photographing obliquely from a high altitude1 thereby increasing the area in the field of vision1 is illustrated by ,figure #ed1 which encompasses ,lake ,erie from one shore to the other and1 in its representation of the main features of the region1 is akin to maps on a relatively small scale1 such as #a3a1jjj1jjj4 #h ,j4 ,w4 ,bagley3 ,the ,use of the ,panoramic ,camera in ,topographic ,surveying1 ,with ,notes on the ,application of ,photogrammetry to ,aerial ,surveys1 ,u4 ,s4 ,geol4 ,survey ,bull4 #feg1 p4 #hd4 8,the scale of the photograph is given by the relation f_/,h1 f being the focal length of the lens and ,h the height of the camera above ground40 7,ibid47 #i ,e4 ,lester ,jones3 ,the ,aeroplane in ,surveying and ,mapping1 ,flying1 ,june1 #aiai1 pp4 #dch-dda1 #dgb1 and #dgf4 #aj ,h4 ,e4 ,ives3 ,airplane ,photography1 #aibj1 pp4 #djg-djh4 #aa ,e4 ,lester ,jones3 ,surveying ,from the ,air1 ,science1 ,vol4 #eb1 #aibj 7,oct4 #ag71 pp4 #egd-ege1 and ,engineering ,news-,record1 ,dec4 #af1 #aibj1 pp4 #aahd-aahf4 #ab ,e4 ,lester ,jones1 op4 cit4 7,science71 p4 #ege4 #ac ,j4 ,volmat3 ,application de la photographie arienne aux levs hydrographiques1 ,comptes ,rendus de l',acad4 des ,sci4 de ,paris1 ,vol4 #afi1 #aiai1 ,oct4 #bg1 pp4 #gag-gah2 idem3 ,rapport sur la mission photohydrographique de ,brest 7#aiai71 ,annales ,hydrogr4 7publ4 by ,service ,hydrographique de la ,marine1 ,paris71 #crd ,series1 #aiai-bj1 pp4 #aia-bbj1 with seven air photographs and corresponding sections from ,french coast charts4 #ad ,h4 ,hamshaw ,thomas3 ,geographical ,reconnaissance by ,aeroplane ,photography1 ,with ,special ,reference to the ,work ,done on the ,palestine ,front1 ,geogr4 ,journ41 ,vol4 #ee1 #aibj1 pp4 #cdi-cgf2 reference on p4 #cfi4