South Dakota School of Mines 5 7 



humus, clearly indicating that this region had not been occupied 

 by a great lake while this stratum was being deposited."* 



A further indication of the non-lacustrine condition, as 

 pointed out by Matthew, is that many of the fossil bones seem 

 to have been uncovered by sediments for a considerable time 

 after the death of the animal. Many porous bones remain un- 

 filled and many others are impregnated with silica rather than 

 mud. The skeletons that remain complete are rare and are 

 commonly much disarticulated. Often projecting portions are 

 lacking, such as the head, the tail or fore limbs or lower part of 

 hind limbs, or the lower jaw, or the ribs. These are the parts 

 most likely to have been originally removed by the vicissitudes 

 of the weather or by the feasting of preying beasts and birds, t 

 Matthew thinks the climate was much as it is today and that 

 wind action was a rather prominent factor in the distribution 

 of the sand and clays and thus -a potent factor in the covering up 

 of the organic remains found in them. 



Mr. Hatcher in his later investigation, although having no 

 belief that the deposits were laid down in a large lake was 

 nevertheless inclined to the idea that climatic conditions were 

 considerably different from that of the same region today and 

 tl> at the surface of the country was possibly not unlike the 

 present extensive marshy flood plains of the upper Amazon, 

 Oronoco, and Paraguay of South America. 



Mr. Gilbert first suggested in 1896 the probable fluviatile 

 origin of the deposits, particularly for those in eastern Colorado. 

 Prof. Davis in 1900 indicated that the capacity of rivers to form 

 extensive deposits of fine texture and even stratification was too 

 frequently underrated and, enlarging upon Gilbert's earlier sug- 

 gestion, directed attention to. the possibility of the Great Plains 

 Tertiary deposits constituting a great piedmont plain of prevail- 

 ing fluviatile origin. Mr. Darton, 1905, considers that during 

 a long period streams of moderate declivity flowed from the 

 west across the region and that these streams with frequently 

 varying channels and extensive local lakes, due to damming and 

 the sluggish flow of the water, laid down the wide-spread 

 mantle of Oligocene deposits, the Brule formation being appar- 

 ently deposited under conditions in which the currents were 

 weaker and the local lakes and slackwater overflows more ex- 



*Am. Phil. Soc. Proc, Vol. 41, 19 02, p.p. 12 6-12 7. 



tiMatthew, W. D. Fos&il Mammals of Northeastern Colorado. 

 Am. ,Mus. Nat. Hist., Mem. Vol. 2, pt. 7, 1901, pp. 359-368. (Condition 

 of deposition.) 



