3-iO Annals of the Carnegie Museum. 



ceramus in sandstones lying above the Marsh (juarry and below the 

 bone-bearing horizon at the " Nipple." These remains, only two in 

 number, were not found in situ, and it is impossible to determine at 

 present the horizon to which they belong. From the general appear- 

 ance of the fragments of sandstone on which they were found I believe 

 they came from the Jurassic, though they may possibly have come 

 from a horizon which by some would be placed in the Dakota, though 

 I must confess my total inability to place any limit to either the top 

 of the Jurassic or base of the Dakota in this region, having experienced 

 the same difficulty encountered by Mr. Darton in the hogback near 

 Buffalo Gap in the Black Hills of South Dakota where he has found 

 dinosaur bones in strata which he thinks may be either Jura or Dakota. 

 I have also examined this latter locality and find the conditions very 

 similar to those in Garden Park and the canon below. I see no more 

 reason for placing the dinosaur beds near Buffalo Gap in the Lower 

 Cretaceous as has been suggested by Darton than for placing those of 

 the region under discussion in the same formation. The difficulty it 

 seems to me lies in the want of a realization of the fact that different 

 conditions prevailed simultaneously over different though often ad- 

 jacent regions and caused the simultaneous deposition of different 

 materials. Along the streams and about the shores of the greater 

 bodies of water deposits of sandstone would predominate, while in the 

 quieter waters and especially off shore the finer materials would be 

 thrown down to form the clays and shales of the same series. Wher- 

 ever we find these shore deposits constituting the Jurassic strata we 

 encounter the same difficulty in separating the Jura from the Dakota, 

 for sedimentation then seems to have been continuous throughout the 

 two periods and we are brought to the question as to the equiva- 

 lents at such localities of the Lower Cretaceous. Could not the rocks 

 of these two formations in part at least represent the fresh water and 

 land equivalents of the marine deposits belonging to the Lower Cre- 

 taceous? Fresh water and marine conditions must have always pre- 

 vailed, as at present, at the same time over different parts of the earth's 

 surface, though thus far there has been little attempt on the part of 

 geologists and paleontologists to correlate them, each series having 

 as a rule been assigned to a distinct period in the time scale, though 

 it is none the less certain that every marine formation has been ac- 

 companied by contemporaneous though more constricted fresh water 

 deposits and that remnants at least of most of such deposits are still 



