28 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND 



the sea. Then after extensive erosion, the sinking of the land and incur- 

 sion of the sea inaugurated another period of geological history. Faunal 

 differences in apparently contemporaneous strata were attributed to the 

 different habitats of the organisms, while the absence of certain strata 

 over wide areas was explained by the erosion during the land interval. 

 The great changes in lithological character from place to place depended 

 upon the topography of the land masses bordering the continental seas. 



In the last decade so many new stratigraphic and paleontologic facts 

 have come to light that the old conceptions regarding stratigraphic corre- 

 lation and the ideas concerning the character and extent of the ancient 

 continental seas have been greatly modified and .often discredited. The 

 lifelong studies of E. 0. Ulrich upon the stratigraphy and paleontology 

 of the American Paleozoic have brought to light new criteria for systemic 

 delimitation, and caused him to propose a revision of the Paleozoic sys- 

 tems based upon these new conceptions. According to his views there 

 never was a vast continental sea of considerable depth enduring through any 

 great period of deposition, nor was there ever any considerable elevation of 

 the adjacent land masses with the consequent erosion, except for compara- 

 tively brief periods. In his work in collaboration with Professor Charles 

 Schuchert, published in Bulletin 52 of the New York State Museum 

 under the title " Paleozoic seas and barriers in eastern North America/' 

 it was brought out that the diastrophic movements producing deformation 

 of the land masses, manifested themselves not only between the larger 

 divisions of geologic time, but even between formations. These move- 

 ments resulted in a north and south warping of the continent with the 

 formation of narrow structural troughs whose position was determined 

 by their location in areas with a predisposition to sink. These troughs 

 or negative areas were separated more or less completely by anticlinal 

 areas which had a positive tendency to remain above sea level in all except 

 the periods of most general submergence. 



These positive and negative areas were discussed in more detail by 

 Schuchert in his great work on the Paleogeography of North America, 

 published in 1910 in the Bulletin of the Geological Society of America. 



