,university of ,texas ,bulletin   ,no4  
#ahba3 ,april #aj1 #aiah       ,fossil  
,ice ,crystals    ,an ,instance of the  
,practical ,value of ,pure ,science     
,illustration3 university emblem        
,bureau of ,economic ,geology and       
,technology   ,division of ,economic    
,geology   ,j4 ,a4 ,udden1 ,director of 
the ,bureau and ,head of the ,division  
,published by the ,university six times 
a month and entered as   second-class   
matter at the postoffice at   ,,austin1 
,,texas     ,publications of the        
,university of ,texas     ,publications 
,committee3    ,f4 ,w4 ,,graff   ,j4 ,m4
 ,,bryant   ,d4 ,b4 ,,casteel           
,,frederic ,,duncalf   ,r4 ,h4          
,,griffith   ,j4 ,l4 ,,henderson   ,i4  
,p4 ,,hildebrand   ,e4 ,j4 ,,mathews    
,the ,university publishes bulletins six
 times a month1 so numbered that the    
first two digits of the number show the 
year of issue2 the last two the position
 in the yearly series4 7,for example1   
,no4 #agja is the first bulletin of the 

year #aiag47 ,these comprise the        
official publications of the            
,university1 publications on humanistic 
and scientific subjects1 bulletins      
prepared by the ,department of          
,extension and by the ,bureau of        
,municipal ,research and ,reference1 and
 other bulletins of general educational 
interest4 ,with the exception of special
 numbers1 any bulletin will be sent to a
 citizen of ,texas free on request4 ,all
 communications about ,university       
publications should be addressed to the 
,chairman of the ,publications          
,committee1 ,university of ,texas1      
,austin4       ,university of ,texas    
,bulletin   ,no4 #ahba3 ,april #aj1     
#aiah       ,fossil ,ice ,crystals      
,an ,instance of the ,practical ,value  
of ,pure ,science     ,illustration3    
university emblem     ,bureau of        
,economic ,geology and ,technology      
,division of ,economic ,geology   ,j4   
,a4 ,udden1 ,director of the ,bureau and
 ,head of the ,division     ,published  

by the ,university six times a month and
 entered as   second-class matter at the
 postoffice at   ,,austin1 ,,texas      
,the benefits of education and of useful
 knowledge1 generally    diffused       
through a community1 are essential to   
the preservation    of a free           
government4                             
,sam ,houston      ,cultivated mind is  
the guardian genius of democracy4444 ,it
 is the    only dictator that freemen   
acknowledge and the only security that  
freemen desire4                         
,mirabeau ,b4 ,lamar     ,,fossil ,,ice 
,,crystals  ,,by ,j4 ,a4 ,,udden  ,,an  
,,instance ,,of ,,the ,,practical       
,,value ,,of ,,pure ,,science   ,the    
practical value of the service of the   
geological profession is1 with every    
year1 being more and more appreciated1  
especially among people who are         
developing the mineral resources of our 
country4 ,nevertheless1 we still hear   
men who speak of geologists as theorists
 that render our profitable industries  

but little assistance4 ,it is true that 
much of the work that geologists do has 
but a remote bearing on practical       
questions4 ,the fact is that in geology1
 as in other sciences1 one can never    
know when a purely scientific           
observation may turn out to have a      
practical application4 ,paleontologists 
who study the minutest details of       
fossils have been held up as impractical
 people1 even though their science has  
more than once proved to be of the      
greatest practical importance for the   
finding of valuable natural deposits4   
,certainly those who have been most     
prominent in the promotion of           
paleontology as a science have seldom1  
if ever1 had any economic motive in the 
pursuit of their work4 ,i think the same
 is true of our leading petrographers4  
,i believe that the men who have        
advanced the science of geology most1   
have seldom contributed much to the     
practical application of the principles 
they have discovered4 ,much scientific  

work naturally appears unprofitable or  
useless to the uninitiated4 ,i shall    
here relate a case that suggests how    
entirely wrong it may be to regard as of
 no economic value any geologic fact1   
however insignificant it may appear4    
,in the summer of #ahij ,i took occasion
 to make a trip to the ,black ,hills in 
,south ,dakota in order to profit1 as ,i
 could1 by a few weeks' tramping in this
 interesting region4 ,going one day in a
 southwest direction from ,minnekahta1  
to look for fossil cycads1 ,i stumbled  
on a block of sandstone with a rather   
smooth surface on which were some       
peculiar markings1 such as ,i had never 
seen figured or described4 ,the rock was
 evidently a block from the ,dakota     
sandstone4 ,its smooth upper surface1   
which represented a bedding plane1 was  
covered with a thin coating of silt or  
fine clay which adhered to the block4   
,the markings were in this clay4 ,they  
were straight1 shallow grooves from     
one-half to two inches in length1 and   

from one-sixteenth to one-eighth inch in
 width4 ,they were joined into patterns 
in which some sprang out from the sides 
of others and again themselves sent out 
other branches4 ,some crossed each      
other4 ,i noticed that there was a quite
 uniform angle of divergence in these   
branches1 and ,i was able to make out   
that this usual angle was about sixty   
degrees4 ,i also noted that the grooves 
narrowed to sharp points4 ,somehow1     
immediately ,i concluded that the cracks
 were the result of ice crystals1 and ,i
 at once saw the propriety of frozen    
water having existed in an age during   
which deciduous trees began to appear4  
,this was theory4 ,we have since that   
time learned to know that cold climates 
far antedate the coming of the          
dicotyledons4  ,as ,i had no suitable   
photographic equipment1 ,i took pains to
 make accurate drawings of a part of the
 pattern as it appeared on the rock4 ,my
 original drawing is shown in ,plate ,i4
 ,a brief description of these markings 

was later furnished in the ,scientific  
,american1 of ,february #ai1 #ahie4  ,it
 took me some years to find any similar 
markings again4 ,in the early spring of 
#aijc ,i had occasion to make a visit to
 ,mexico1 when ,i spent a half day in   
,ojinaga1 which is a little village     
south of ,presidio1 in ,texas1 on the   
,mexican side of the river4 ,some       
sidewalks in this little village are    
built of flags of limestone belonging to
 the ,eagle ,ford formation4 ,to my     
great delight ,i found some of these    
slabs having precisely the same kind of 
markings that ,i had noted on the       
sandstone in ,dakota4 ,naturally ,i     
attached some importance to the fact    
that the ,eagle ,ford corresponds quite 
closely in age to that of the ,dakota   
sandstone4 ,both were made at about the 
beginning of the upper ,cretaceous age4 
,i noticed here a considerable variation
 in the closeness of the patterns of the
 markings4 ,occasionally they were found
 as separate single lines1 several      

inches removed from each other2 and on  
other rocks they would be found crossing
 in close networks4 ,in the summer of   
#aijd ,i again found my ice markings on 
a layer of arenaceous limestone in the  
same formation in the ,big ,bend country
 in ,texas4 ,this time ,i collected some
 specimens which were subsequently      
photographed4 ,one of these photographs 
is shown in ,plate ,,ii4 ,again in #aijf
 ,i noticed the same markings on some   
thin sandy flags which occur in the ,del
 ,rio clay near the city of ,del ,rio4  
,in this case the needle-like crystals  
were somewhat more slender than those   
previously seen1 and some were slightly 
curved and somewhat more elongated4     
,these of course interested me as       
showing the occurrence of freezing      
temperatures no doubt at a somewhat     
earlier time than that pertaining to my 
previous observations4  ,during all     
these years my residence was in         
,illinois1 and ,i was naturally watching
 for similar markings in recent mud1    

resulting from late and early frosts4 ,i
 found them in the fall of #aiji4 ,at   
this time some excavations were being   
made in the loess in ,rock ,island1 when
 some rains fell in the late fall4      
,these rains evidently happened to give 
the mud the amount of moisture necessary
 for such crystals to develop1 as the   
ground froze4 ,the rains had washed the 
loess extensively1 and ,i found a number
 of places where it lay redistributed1  
with a fairly smooth surface4 ,it was   
evident that the moisture content of the
 ground1 together with the temperature  
conditions1 determined the size and the 
closeness of the frozen patterns4 ,in   
places the crystals were long and       
slender1 in others they were short and  
stout4 ,at some points they were        
straight and in others slightly curved4 
,here and there the patterns were close 
enough to resemble the fine lines which 
we sometimes notice in the hoarfrost on 
windowpanes4 ,in other places the       
crystals occurred in radiating groups1  

and elsewhere they would form scattered 
separate units4 ,for preserving a record
 of what ,i saw1 ,i poured plaster over 
several patterns and had these casts    
photographed1 as appears in ,plates     
,,viii1 ,,ix1 ,x4 ,placing these side by
 side with the photographs of the       
patterns ,i have photographed from the  
,eagle ,ford1 it appears to me that no  
doubt can be left as to the origin of   
the markings found in the fossil state4 
,recently ,i have found that these ice  
crystal marks are quite common at one   
horizon in the ,eagle ,ford beds of     
,brewster ,county1 in ,texas4 ,there is 
also a layer in which they can be       
usually seen in the vicinity of ,austin1
 ,texas4 ,this lies about twenty-five   
feet below the ,austin ,chalk1 near     
,austin4 ,a like layer occurs about #ajj
 feet below the ,austin ,chalk in the   
,big ,bend country4 ,here ,i have found 
the markings in localities thirty miles 
apart4 ,they occur at the north point of
 ,mariscal ,mountain and in a number of 

places near the ,fossil ,knobs and on   
the ,chisos ,mining ,company property at
 ,terlingua4  ,unprofitable as          
observations on such a simple matter as 
this may seem1 ,i find that other       
geologists have given it some attention4
 ,quite recently1 ,dr4 ,john ,m4        
,clarke,a has figured slabs showing what
 has been described as ,fucoides        
graphica1 by ,hall4 ,the markings       
figured by ,professor ,clarke are       
undoubtedly of the same kind as those ,i
 have found in the ,eagle ,ford4 ,they  
occur in the ,upper ,devonian in ,new   
,york4 ,i also find that the formation  
of ice crystals in wet mud has been     
observed in the clays about ,boston by  
,marbut and ,woodworth4,b ,other        
observations of similar recent markings 
are said to have been made by some      
,english geologists4  ,to practical     
people it may indeed appear that no more
 unprofitable or more idle curiosity    
could be indulged in1 than making       
observations on what kind of crystals   

are formed when water freezes in mud4 ,i
 must confess that my own first         
observations had no motive whatever1    
except for the desire to know something 
new2 and ,i never expected that anything
 ,i could learn about these fossil marks
 would ever turn out to have any        
practical application1 at least not in  
my own work4  ,but it has turned out    
differently4 ,for some time1 ,i have    
been called upon occasionally to advise 
with regard to the finding of the ore in
 one of our quicksilver mines in ,west  
,texas4 ,it is now a well established   
fact that the distribution of the ore in
 this mine1 and ,i believe in the entire
 ,terlingua district1 bears a definite  
relation to geological horizons4        
,successful mining requires search in   
these horizons4 ,the cinnabar1 as it    
appears1 has accumulated in greatest    
quantity under impervious rocks such as 
shales and marls along planes that      
separate these from underlying rocks of 
more open texture1 mostly limestones4   

,the ore has clearly come from below and
 has risen through fissure planes1 which
 in some cases separate large blocks of 
the ,cretaceous formations4 ,the best   
ore has been found under the basal part 
of the ,boquillas flags1 and under the  
,del ,rio clay in the upper part of the 
,georgetown limestone4 ,the workings    
must be so arranged in the mine that    
these horizons can be entered on both   
sides of a fault fissure4 ,the problem  
of locating the depth of the desirable  
horizons in the mine in question would  
be easy enough1 if it were not for the  
fact that the outcropping rocks consist 
of a series of sediments with few       
characteristic fossils4 ,most of the    
fossils which occur extend through a    
range of several hundred feet and the   
beds themselves are quite uniform in    
character1 consisting of alternating    
thin layers of impure limestones and    
marls4 ,an attempt was made to correlate
 the outcropping beds by close          
examination of the layers exposed1 but  

the result was not very satisfactory4 ,a
 close scrutiny made of each layer on   
the section resulted1 however1 in the   
finding of two features that enabled me 
to measure the throw of the fault under 
investigation4 ,interbedded in the      
,boquillas flags there are some thin    
layers of bentonite1 which are quite    
persistent and can be followed for      
several miles4 ,by comparing the        
distances between these layers and by   
taking note of their individual         
thickness1 it was possible to make a    
correlation that seemed to be correct4  
,but the proof sought fell just short of
 being certain4 ,in cases of this kind  
one always looks for corroborating facts
 to check one's conclusions4 ,i found   
this check in the discovery of the layer
 which carries ice crystal markings in  
these beds4 ,the layer had a definite   
relation to the seams of bentonite1 and1
 with this additional evidence1 ,i was  
confident there was no possible chance  
of a mistake4 ,it enabled me to locate  

not only the right horizon but also a   
horizon in the underlying heavy         
,comanchean limestone1 which is         
water-bearing1 and which must be avoided
 to prevent serious injury to the       
underground operations4 ,i need not add 
that the information obtained was of    
real practical value in this case4      
,,plate ,i   ,plate ,i4 ,forms of frost 
cracks seen on the exposed flat bedding 
plane of a block of ,dakota sandstone in
 a ravine a few miles southwest of      
,minnekahta1 ,south ,dakota4 ,as        
sketched in the field4 ,natural size4   
,illustration3 ,,plate ,i     ,,plate   
,,ii   ,plate ,,ii4 ,photographs of     
fossil imprints of ice crystals on flags
 of the ,eagle ,ford4 ,the upper rock   
shown in the ,plate is from the south   
side of ,cuesta ,blanca in ,brewster    
,county1 ,texas1 and shows casts of     
crystals which represent fillings of    
sandy mud projecting slightly down into 
an underlying bed of more argillaceous  
material4 ,the lower part of the figure 

shows a similarly marked flag from the  
same formation at a point about five    
miles north of the old ,boquillas       
postoffice near ,tornillo ,creek1 east  
of the ,chisos ,mountains1 in ,texas4   
,here are seen the original grooves made
 by the ice on a layer of muddy material
 later buried4 ,slightly reduced4       
,illustration3 ,,plate ,,ii     ,,plate 
,,iii   ,plate ,,iii4 ,photograph of    
fossil casts of a close tangle of ice   
crystals seen in a stony calcareous     
layer in the ,eagle ,ford shale in      
,walnut ,creek1 about eight miles north 
of ,austin1 ,texas4 ,this tangle is     
closer than any of the recent ice       
crystal marks figured here1 but equally 
closely grown crystals have been seen by
 the writer on frozen mud in ,illinois4 
,natural size4 ,compare with ,plate     
,,viii4  ,illustration3 ,,plate ,,iii   
,,plate ,,iv   ,plate ,,iv4 ,photograph 
of fossil casts of ice crystals seen on 
some stony flags in the upper part of   
the ,eagle ,ford at ,fossil ,knobs1     

about two miles northwest of the ,chisos
 ,mine in ,brewster ,county1 ,texas4    
,these may be characterized as          
relatively short and scattered4 ,this   
shows ridges projecting into the grooves
 formed by ice crystals on the surface  
of a muddy layer originally underlying  
the layer photographed4 ,slightly       
reduced4  ,illustration3 ,,plate ,,iv   
,,plate ,v   ,plate ,v4 ,photograph of  
fossil casts of ice crystals seen on the
 under side of flaggy layer of          
calcareous sandy rock in the upper part 
of the ,eagle ,ford at ,fossil ,knobs1  
about two miles northwest from the      
,chisos ,mining ,company's property1    
,brewster ,county1 ,texas4 ,it will be  
seen that some of the crystals are      
gently curved4 ,similar curving crystals
 are also seen in the figures showing   
recent growths at ,rock ,island1        
,illinois4 ,compare with ,plate ,,ix4   
,slightly reduced4  ,illustration3      
,,plate ,v     ,,plate ,,vi   ,plate    
,,vi4 ,photograph of a thin flag of     

sandy limestone from the ,eagle ,ford at
 ,fossil ,knobs in ,brewster ,county1   
showing molds left by ice crystals4     
,illustration3 ,,plate ,,vi     ,,plate 
,,vii   ,plate ,,vii4 ,photographs of   
three fragments of flags showing casts  
of ice crystals on the under side4 ,all 
observations made on crystals of this   
kind indicate local differences in the  
forms of ice crystals presumably due to 
differences in the rate of freezing1 in 
the texture of the mud and probably in  
variations in water content of the mud4 
,some crystals in the locality from     
which these specimens came1 show pinnate
 secondary growths4 ,specimens shown    
here are from near the upper part of the
 ,eagle ,ford at a point about two miles
 north from the ,chisos ,mining         
,company's property4 ,brewster ,county1 
,texas4 ,slightly reduced4              
,illustration3 ,,plate ,,vii     ,,plate
 ,,viii   ,plate ,,viii4 ,photograph of 
a cast made by pouring plaster over a   
surface of mud in which ice crystals had

 recently formed1 in ,rock ,island1     
,illinois1 after the ice in the crystals
 had been removed by slow natural       
sublimation into the atmosphere1 leaving
 open cracks in the mud4 ,the comb-like 
ridges on the plaster cast have the form
 of the ice crystals4 ,compare with     
,plate ,,iii4  ,illustration3 ,,plate   
,,viii     ,,plate ,,ix   ,plate ,,ix4  
,photograph of a cast made by pouring   
plaster over a surface of mud in which  
ice crystals had formed1 in ,rock       
,island1 ,illinois1 soon after the ice  
in the crystals had been removed by slow
 natural sublimation into the           
atmosphere1 leaving open cracks in the  
mud4 ,in the locality where this cast   
was made1 the crystals were relatively  
slender1 distant1 and some gently       
curved1 like those seen in ,plate ,v4   
,slightly reduced4  ,illustration3      
,,plate ,,ix     ,,plate ,x   ,plate ,x4
 ,photograph of a cast made by pouring  
plaster over a surface of mud in which  
ice crystals had recently formed1 in    

,rock ,island1 ,ill41 and where they had
 later been removed by natural          
sublimations into the atmosphere1       
leaving open cracks in the mud4 ,it will
 be seen that the crystal growth in this
 case involves an x-like or radiating   
pattern formed of relatively very       
slender forms that almost everywhere are
 very gently curved somewhat reminding  
of the slender thread-like crystals     
sometimes seen in frost on windows4 ,i  
have not yet seen any similar fossil    
crystal growths as slender as these4    
,slightly reduced4  ,illustration3      
,,plate ,x     ,,footnotes3   ,a ,strand
 and undertow markings1 etc41 ,new ,york
 ,state ,museum1 ,bulletin ,no4 #aif1   
,april #a1 #aiag1 pp4 #aii-baj2 pl4     
#bj-bc4  ,b ,brick clays of ,rhode      
,island1 ,massachusetts2 ,marbut and    
,woodworth1 ,u4,s4 ,geol4 ,survey1 #agth
 ,ann4 ,rep41 ,pt4 #a1 p4 #iib4         
,transcriber's ,notes3   ,passages in   
italics are indicated by underscore4    
,printer's inconsistencies in spelling  

and punctuation have been retained4