1904.] HATCHER MARINE AND XOX-MARIXE FORMATIONS. 359 



brought about simultaneously over this entire region, conditions 

 however which are absolutely prohibited by any even fairly reason- 

 able hypothesis. It seems quite reasonable therefore to suppose 

 that the early Laramie was largely contemporaneous in origin with 

 the later Pierre, and were the geological records complete it is not 

 impossible, and I may say improbable, that somewhere to the west- 

 ward of the iioth meridian the wedge of Pierre shales interposed 

 between the Judith river beds below and the Laramie above would 

 thin out and become entirely replaced by these two formations, just 

 as the Judith river beds below pass into the overlying and underly- 

 ing marine deposits to the eastward of that meridian. 



From the nature of the terrestrial and fresh water vertebrate and 

 invertebrate faunas of the various deposits represented in this region, 

 from the base of the Atlantosaurus beds below to the summit of the 

 Laramie above, it is evident that somewhere in this region or adja- 

 cent to it terrestrial and fresh water conditions prevailed continu- 

 ously throughout this entire period though perhaps not in any one 

 locality. Although we have at present only a partial record of such 

 terrestrial conditions it is probable that the record may be still 

 further perfected by the discovery of remnants at least of other non- 

 marine formations. 



From the above remarks it will, I think, have been made clear that 

 the various non-marine Jurassic and Cretaceous deposits of our 

 Middle West do not necessarily represent time intervals distinct 

 from those which witnessed the deposition of the marine beds of 

 the same region, but that marine and terrestrial conditions existed 

 simultaneously and more or less continuously, each giving origin to 

 its peculiar deposit. It thus happens in this region that every non- 

 marine deposit, save the uppermost Laramie, has its marine equiva- 

 lent with which by careful study it may be correlated, and the 

 following diagram' is submitted as representing the author's present 

 views as to the proper correlation of these deposits. 



1 The diagram as originally prepared has been altered slightly, as follows : The 

 Laramie is made to extend over the Montana group ; the Claggett formation is 

 made to blend with the Pierre-Fox Hills beyond the limits of the Judith River 

 beds; and the Niobrara is interpolated between the Benton shales and the Mon- 

 tana group. These changes make the diagram agree with the text. — T. W. S. 



