August 9, 1901.] 



SCIENCE. 



211 



Hatcher, of the Carnegie Museum ; with 

 the party was also Professor Eberhard 

 Fraas, of Stuttgart. The object of the ex- 

 pedition was to secure exact geological data 

 for the monograph ' The Titanotheres,' 

 now in preparation by Professor Osborn. 

 The matters of chief importance were : 

 first, to determine the mode of deposition of 

 these beds in view of the arguments re- 

 cently brought forward by Matthew, Davis 

 and others that they were seolian rather 

 than aqueous in origin ; second, to deter- 

 mine the exact stratigraphical levels upon 

 which the different types of skulls and 

 skeletons have been found, verifying and 

 extending the very careful records made by 

 Mr. Hatcher between 1886 and 1888 while 

 collecting for the United States Geological 

 Survey, under Professor Marsh. 



Mr. Darton will prepare the formal re- 

 port of the geological results of this expedi- 

 tion, including a map showing the extent 

 and exact thickness of the beds in differ- 

 ent portions of this region. In the mean- 

 time it is interesting to learn the opinions 

 of a highly trained European geologist, 

 Professor Fraas, upon the nature of these 

 beds, expressed in an informal letter to 

 Professor Osborn : 



" I take this opportunity to briefly pre- 

 sent my opinion on the origin of the Oligo- 

 cene of the Bad Lands. So far as I have 

 been able to observe the beds during the 

 past eight days, one can by no means speak 

 of their structure as feolian in the ordinary 

 sense of the word. It is quite possible that 

 wind-transport may have taken some part 

 in their formation, but the strata themselves 

 appear to me to have been chiefly laid 

 down under water. We ought, I think, to 

 take into consideration the following series 

 of different petrographical and structural 

 conditions : 



" (1) The Titanotherium Beds, which con- 

 stitute the base of the Oligocene, I take to be 

 the deposit of a slowly flowing river, which 



emptied in the broad delta upon the level 

 stretches of the Ft. Pierre [Middle Cretace- 

 ous] . This view is supported by the oc- 

 currence of large boulders of ground-con- 

 glomerate at the base of the Titanotherium 

 Beds, as well as by the frequent embedding 

 of sand and gravel in the clays and marls. 

 The current was manifestly very gentle 

 and laid down a continuous substratum, 

 resulting in cross-bedding in the sands 

 and gravels. Against the dune-structure 

 (feolian) testify the widespread layers- 

 of sand banks, often very thin, the heavy 

 gravel and the fine lamination of the clays. 

 The current was directed from west to east,. 

 and corresponding to this the thickness of 

 the gravel and sand layers diminishes as 

 we pass eastwards. (2) It is very difficult 

 to determine the origin of the overlying 

 Oredon Beds [Middle Oligocene, 560 feet 

 in thickness]. We must take the follow- 

 ing facts into consideration : (a) The entire 

 material has undergone a strong' meta- 

 morphosis ; the sandy, non- calcareous clays 

 were formerly marls rich in calcareous 

 matter, the concretionary structure of the 

 harder banks and the texture of the material 

 giving positive evidence on this point. (6) 

 Certain layers were very rich in gypsum 

 and barite ; both minerals are now repre- 

 sented only in pseudomorphs of chalcedony, 

 formed out of gypsum and barite. Probably 

 there was united with the tendency to gyp- 

 sum formation, a similar tendency to rock- 

 salt formation, but I have found no evidence 

 of this, (c) The structure of the layers: In 

 the Loiver Oreodon Beds concretions are abun- 

 dant, which originally were composed of 

 clays rich in calcareous matter. (This is- 

 the principal layer of Testudo and of the 

 mammals.) Here are also thin banks of 

 clear limestone, now strongly silicified ; 

 land and fresh water snails are found here 

 (Helix and Limmea) ; sand layers are not 

 found here. The very massive Middle 

 Oreodon Beds are splendidly laminated and 



