1904.] HATCHER — MARINE AND NON-MARINE FORMATIONS. 355 



From the foregoing remarks it will appear that in the region 

 referred to in the title of this paper there is a conformable series of 

 marine and fresh water or in part aeolian deposits, commencing 

 below in the north with marine beds unquestionably of Jurassic age 

 and passing upward and toward the south and east into a series of 

 fresh water and aeolian deposits containing adinosaurian fauna, with 

 affinities clearly allying it also with the Upper Jurassic and another 

 still later horizon, the Lakota of Darton, with a Lower Cretaceous 

 flora and a dinosaurian fauna of the character of which as yet little 

 is known, but which is certainly more recent than that of the true 

 Atlantosaurus beds, the entire series terminating above in the 

 Dakota sandstones generally referred to the base of the Upper Cre- 

 taceous. This entire series rests unconformably upon the ''Red 

 Beds" in such manner as to show conclusively that prior to the 

 beginning of its deposition there was in this region a long and con- 

 tinued period of erosion, embracing perhaps the close of the 

 Triassic and a considerable portion of the Jurassic. At the top the 

 Dakota sandstones are overlaid with apparent conformity by the 

 Benton, the lowermost marine member of the Upper Cretaceous. 

 As yet no evidence has been advanced to show that sedimentation 

 was not continuous in this region from that period which marked 

 the beginning of the deposition of the marine Baptanodon beds at 

 the base of the series to the close of that much later period which 

 witnessed the deposition of the Dakota sandstones, and I see no 

 reason why this series of deposits may not represent in this region 

 the entire Lower Cretaceous and Upper Jurassic, as their floras and 

 faunas and the stratigraphy and conditions of sedimentation would 

 seem to indicate. I am well aware of the enormous time interval 

 which a correlation such as that just suggested presupposes for the 

 deposition of this comparatively meagre series of deposits, aggregat- 

 ing a thickness nowhere of perhaps as much as looo feet and in no 

 way comparable with the thousands of feet of beds which in other 

 regions are known to be included in the Lower Cretaceous alone, to 

 say nothing of the Upper Jurassic. Nevertheless this objection 

 does not seem an especially important one when we consider the 

 wide geographical distribution of those non-marine deposits which 

 constitute by far the greater bulk of this series, and the time 

 interval necessary for the deposition of which, as we have seen at 

 the beginning of this paper, should be estimated not so much by 

 their vertical thickness as by the extent of their geographical dis- 

 tribution. 



