90 Reviews — Devonian System in Maryland. 



the similarity of the conditions under which they were deposited, 

 the chief diiference being the development of the Keyser Limestone in 

 Maryland, an earlier phase of the Helderberg than has hitlierto 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 

 Maryland, clays being deposited near the shore in Onondaga time, 

 while limestone was formed in the open sea farther west. . . . 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, 

 Hypothjris cuboides, is found at such widely separated points as New 

 York, North- Western America, the Rhine Province, Russia, and 

 China. It seems, therefore, to have encircled the northern hemi- 

 sphere 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 descendants 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 diifered greatly from 

 all that preceded them in this region. They consist chiefly of 

 Goniatites (Cephalopods with angular sutures) and minute Pelecypods. 

 The rarity of Brachiopods is conspicuous. This assemblage, termed 

 by [J. M.] Clarke the Naples fauna (also known as the Intumescens 

 fauna from its guide species, Manticoceras intumescens), is believed 

 by him to have journeyed from its home in north-eastern Arctic 

 Russia via north-western 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 development of the species. . . . As the 

 level of the sea oscillated, leading to the interleaving of the two 

 types of containing sediments in central New York, the Naples and 

 Ithaca faunas migrated back and forth. That these faunas ranged 

 southward into Maryland is shown by the occurrence of the Naples 

 fauna in abundance in the Genesee and lower beds of the Woodmont 

 member of the Jennings formation of the western sections and the 

 replacement of the Naples fauna by the Ithaca fauna in the upper 

 beds of the Woodmont member of the eastern sections, while it still 

 continued to live in the west, indicating conditions essentially 

 similar to those that existed in New York at this time. It results 

 that three independent faunas coexisted in this province in earlv 

 Upper Devonian time, their range being determined by the physical 

 conditions under which they dwelt, while they migrated back and 

 forth as these conditions varied." 



Other instances of the introduction, survival, and recurrence of 

 species are discussed ; and it is pointed out that towards the close 

 of the Devonian period the land was elevated, and the thick deposits 

 of red clays and sands of the Catskill formation were accumulated 

 in lakes and embayments. The strata contain macerated remains of 

 plants and fragments of fishes. " The Devonian was finally terminated 



