364 HATCHER — MARINE AND NON-MARINE FORMATIONS. [April 7, 



Concerning two important assumptions in Hatcher's argu- 

 ment we could not reach an agreement : (i) That the continuance 

 of present conditions along the Atlantic coast would result in such 

 a succession of formations as is represented by Fig. i ; and (2)|that 

 the conditions now obtaining along this coast are comparable to 

 any considerable extent with those of the Middle West in Mesozoic 

 time. 



The diagram (Fig. i) was of course intended only as a crude 

 illustration of the author's ideas. Granting that the littoral 

 deposits might extend progressively seaward over the true marine 

 beds, it is scarcely conceivable that the sediments laid down in 

 brackish and fresh waters could constitute continuous formations 

 across the entire area, nor that any great thickness of fresh water 

 deposits could be built up above sea level on a coastal plain. 

 Nor does it seem to me probable that even the littoral deposits laid 

 down under such conditions would be treated as a single formation. 



It is difficult to reconstruct the physiographic conditions that 

 prevailed in the middle West during later Mesozoic time, but it 

 should be remembered that there was then a great shallow continental 

 or mediterranean sea, and that there were large areas so near sea 

 level that very slight movements would bring them beneath the sea 

 or partly or wholly drain them, so that it is probable that shallow 

 water and non-marine conditions were often extended over large 

 areas very rapidly. It should be remembered also that in speaking 

 of the great geographic distribution of the resulting formations we 

 are often dealing with their extension along a shore, or with con- 

 temporaneous deposits on opposite shores of the same sea. With 

 such conditions it is easy to understand the many alternations of 

 marine with non-marine formations, and it is recognized that both 

 classes of deposits were formed contemporaneously in adjacent areas. 

 This has made the geologic record of that region very complex, if 

 not obscure, and it is still far from being completely interpreted. 



The correlations indicated by the diagram have mostly been 

 worked out by stratigraphic methods aided by paleontology, and 

 agree with the present state of knowledge so far as the Upper 

 Cretaceous is concerned. The treatment of the lower horizons is 

 more tentative and represents Hatcher's opinions as stated in the 

 text. 



More detailed criticism and comment are unnecessary, although 

 many minor points are subject to discussion. The whole paper is 



