E. M. Kindle — Bottom Control of Marine Faunas. 461 



very certain to be rich in molluscan shells. A hypothetical 

 East-arid -West cross section through the present mouth of the 

 estuary in the year 10000 it may be inferred would show at the 

 base a lens of sandstone one half mile wide and about 20 7 thick 

 absolutely barren of fossils. Flanking and covering this bar- 

 ren sandstone would be a fossiliferous sandy shale resting on 

 a fossiliferous conglomerate with a fauna closely allied to the 

 shaly fauna above. It should be noted here that the materials 

 for the barren sandstone and the fossiliferous conglomerate 

 alongside it are already in place and are not hypothetical. Is 

 it not probable that the astute geologist of this future time 

 might conclude that the barren sandstone was separated from 

 the fossiliferous conglomerate and shale by an unconformity 

 and so infer an uplift followed by subsidence where there had 

 been only uninterrupted subsidence ? A mile or two from this 

 hypothetical section he would find sections of shale containing 

 very few fossils except U-shaped burrows made by a small 

 crustacean, Oorophium volutator (Pallas). Thousands of these 

 would characterize every cubic yard of the shale and he might 

 easily fail to realize that these brackish water beds, the shales 

 and conglomerate with a marine fauna and the barren sand- 

 stone, represented different facies of the same stage of sedi- 

 mentation. 



It is pleasing to note, however, that there is a growing tend- 

 ency on the part of paleontologists to give consideration to 

 the ecological conditions under which fossil faunas lived. 

 Twenhofel's work on "The Anticosti Island Faunas "* is an 

 example of this tendency. He finds in Anticosti that " the 

 faunas of the north and south shores show great differences 

 which in every instance correspond to differences in lithology 

 and hence to differences in the ecologic conditions at the time 

 of sedimentation." 



It is of the utmost importance that the paleontologist in 

 using fossils for correlation should recognize and bear in mind 

 the close relationship between the physical texture of the bot- 

 tom and the kind of life living upon it. Recognition of this 

 relationship will in no wise restrict him in using similarity 

 of faunas as evidence of age equivalence in beds of similar 

 lithologic type, but it should teach him to be extremely cautious 

 when dealing with unlike lithologic types, in attributing dif- 

 ferences between faunas to differences in age if etratigraphic 

 considerations do not support such an inference. Instead of 

 expecting the same type of fauna in synchronous deposits of 

 widely unlike lithology he should look for faunal contrasts in 

 which the faunal facies varies as widely as the lithologic facies. 



Victoria Memorial Museum, Ottawa, Canada. 



*Can. Geol. Survey Mus. Bull., No. 3, pp. 2, 11, 1914. 



