162 ANNALti NEW YORK ACADEMY OF SCIENCES 



in this locality was cut off. The period following was one of greater 

 changes and probably of slower deposition than that preceding the river 

 period. The presence of fine reeds or sedges shows that the water was 

 shallow, at least in places, and parts of skeletons found on irreguliar sur- 

 faces imbedded in these reedy clays suggest mud-bars or islands, on 

 which they have stranded. In one instance part of a skeleton found 

 imbedded in a stratum of blue clay which thinned out and was replaced 

 by sandstone with pebbles at the base, indicates that the carcass was 

 buried in a mud-bank bordering a stream or water-current. The inter- 

 ruption of the vertebral column and the displacement of the ribs in one 

 direction show that the stream was sufficient to carry away the missing 

 part of the skeleton. 



"The tendency toward a more shaly nature and the presence of car- 

 bonaceous matter in the upper measures indicate the return of shallows 

 and the greater abundance of vegetable matter. This condition evidently 

 culminated in the great influx of sand laden with deciduous leaves which 

 marks the period represented by the Dakota sandstone." 



Loomis (1901, 6) discussed the Morrison in the Como Bluff region. 

 He referred to the beds as "non-marine Jura," and later in the same 

 paper stated that the shore line, which was about 30 miles south of Como 

 Bluff during Shirley or Sundance time, moved 100 miles to the south at 

 the beginning of Como or Morrison time, and that the deposits were then 

 laid down in shallow water; also that "the bones [of dinosaurs] are 

 clearly floated out to sea by the presence of considerable meat on them." 

 There is thus an element of contradiction in Loomis's interpretation. 



Hatcher (1903, 4) discussed the origin of the Morrison at some length. 

 As his conclusions are closer to those of the present writer than those of 

 any of the other workers mentioned, the important parts of his discus- 

 sion will be quoted at this point. 



"I can fully agree with Dr. White as to the necessity of assuming the 

 existence in Jurassic times of a continental land-mass of the dimensions 

 intimated in his paper. But it does not seem to me at all necessary to 

 presuppose the existence of a Jurassic lake of even the smaller or more 

 moderate dimensions assigned by him. While I do not wish to be under- 

 stood as denying the possi1)ility of the existence of a great lake in Jurassic 

 times extending as Dr. White has suggested from the x\rkansas River 

 in Colorado to the Black Hills of South Dakota, it does appear to me that 

 our present knowledge of the character of the faunas, both terrestrial and 

 aquatic (fresh-water) as well as of the lithologic and stratigraphic fea- 

 tures exhibited by the beds themselves is decidedly against such a pre- 

 sumption. If I properly understand Dr. White he finds nothing in the 



