Maryland Geological Survey 27 



which they were deposited, the chief difference being the development of 

 the Keyser limestone in Maryland, an earlier phase of the Helderberg than 

 has hitherto been recognized in New York, and the profusion of life in 

 the Oriskany. In Lower Devonian time' the Helderberg and Oriskany 

 seas stretched southward from New York to beyond Maryland. The Middle 

 Devonian was ushered in by a slight deepening of the seas in ]\rar}'land, 

 clays being deposited near the shore in Onondaga time, while limestone 

 was formed in the open sea farther west. The shales were long believed to 

 be of Marcellus age but have since been shown by Kindle to have been 

 formed in Onondaga time. The Marcellus and Hamilton sediments of 

 Maryland so closely resemble those of New York in their lithology and 

 their forms of life as to leave little doubt that they were deposited in the 

 same basin and under similar conditions. 



The Upper Devonian introduces one of the most interesting chapters 

 of the history of this period. At the beginning of Upper Devonian time 

 a fauna appears comprising few species, one of which, Ilypothyris 

 cuboides, is found at such widely separated points as New York, north- 

 western America, the Ehme Province, Russia, and China. It seems, 

 therefore, to have encircled the northern hemisphere in its journeys. The 

 cuboides fauna lasted but a short time. In later Middle Devonian time 

 the sea had deepened throughout the west in North America. The de- 

 scendents of the Middle Devonian shore-loving brachiopods of the eastern 

 area continued to live in the shallower waters where they received 

 new species from the Atlantic and by their combination formed the 

 Ithaca fauna. The deeper waters off shore were invaded by forms that 

 differed greatly from all that preceded them in this region. They consist 

 chiefly of goniatites (cephalopods with angular sutures), and minute 

 pelecypods. The rarity of bracliiopods is conspicuous. This assem- 

 blage, termed by Clarke the Naples fauna," is believed by him to have 

 journeyed from its home in northeastern Arctic Russia via northwestern 

 America to New York and eastward to the Rhine Valley where it is found 

 in a similar position, its route being indicated by the progressive develop- 



' See Schuchert's discussion of Paleogeography in this volume. 

 = N. Y. State Mus. Mem. No. 6, 1903. This fauna is also known as the Intu- 

 mescens fauna from its guide species, Manticoceras intumescens. 



