348 HATCHER — MARINE AND NON-MARINE FORMATIONS. [April 7 



shore line, a section tlirough the deposits formed before and during 

 this period would exhibit a structure similar to that shown in the 

 second diagram, where A. represents a wedge of fresh water depos- 

 its immediately overlaid and underlaid by the brackish water beds 

 B. B., followed above and below by the littoral deposits C. C, 

 which are in turn underlaid and overlaid by the true deep water 

 marine beds D. D., and the time interval during which the single 

 fresh water formation represented by A. was deposited will have 

 equaled that employed in the deposition of the underlying and 



Fig. 2. 



overlying marine and brackish water beds combined. The fresh 

 water beds should, therefore, be correlated with both the underly- 

 ing and overlying marine beds. 



The actual conditions at present existing along our Atlantic 

 coast, together with the possible results following a long continu- 

 ance of these conditions, with variations similar to those outlined 

 above, have evidently been repeated at certain intervals in Mesozoic 

 times throughout our Middle West. 



The Judith river beds at about the middle of the Upper Creta- 

 ceous, together with the overlying and underlying marine forma- 

 tions, known respectively as the Pierre or Bearpaw shales and the 

 Claggett formation, form a splendid example of the conditions 

 illustrated in the second diagram. They are composed of a series 

 of deposits for the most part of fresh water origin, but overlaid and 

 underlaid by brackish water beds. They attain to a known thick- 

 ness of something over 500 feet and extend continuously from the 

 Saskatchewan river region in Canada to southern Montana. They 

 are well developed along about the iioth meridian of west longi- 

 tude, where they may perhaps be regarded as attaining their maxi- 



