E. 31. Kindle — Criteria of Continental Deposits. 227 



waters of moderate depth. It occurs even in limestones. The 

 writer has seen excellent examples of cross-bedding in the 

 Spergen limestone of Indiana. We believe that no one, not 

 even Professor Grabau, will question the marine origin of the 

 Spergen limestone. If geologists will bear these facts in mind 

 they will neither cite cross-bedding in rocks as an evidence of 

 their origin in continental waters nor in extremely shallow 

 marine waters as is often done. 



Critical inspection of the other criterion of n on marine sedi- 

 ments referred to by Professor Grabau shows it to be fully as 

 untrustworthy as cross-bedding, as a means of discriminating 

 nonmarine beds. Making use of the absence of fossils from 

 any given bed, whether partial or total, as evidence of its non- 

 marine origin rests upon a serious misconception of the facts 

 relating to the distribution of both extinct and living molluscan 

 forms. Marine animals with hard structures were not uni- 

 formly distributed over the epicontinental sea bottoms in the 

 past, nor is the present sea bottom within the life zone of the 

 continental shelf occupied with anything like uniformity. Off 

 some of our present coasts richly tenanted areas alternate with 

 others which are barren of life. The occurrence of barren 

 zones in both present and Paleozoic seas, instead of being an 

 improbable or anomalous thing, as Dr. Grabau's remarks 

 would indicate, is a fact which may be easily demonstrated. 

 This fact requires no " laborious explanation," but is a corollary 

 of the familiar principle that the distribution of marine life is 

 controlled by environmental factors, among which are tempera- 

 ture, food, salinity, protection from destructive wave action, 

 and transportation of larval forms. Ocean currents frequently 

 control, partially or completely, one or more of these factors 

 with the result that adjacent areas of the same sea may be on 

 the one hand marine deserts and on the other areas teeming 

 with marine life. 



Among the factors controlling faunal distribution, least likely 

 to impress the paleontologist with their great importance if 

 his acquaintance with the seashore is limited, is the character 

 of the bottom, depth, and exposure to storm waves. Mr. God- 

 win-Austen* has well said that a " drift sand zone " is wholly 

 unfitted for marine life. It can be easily imagined that it 

 would be as difficult for a molluscan fauna to secure a foothold 

 on the shifting sands of some coasts as it is for terrestrial life 

 to establish itself firmly in a sand-dune country. If, to the 

 probability of being buried alive, we assume complete exposure 

 to the direction of the heaviest gales and a depth which will give 

 to storm waves their maximum destructive effect in pounding 

 the bottom, we will have an environment in which no molluscan 

 * Natural History of the European Seas, p. 233. 



