82 AMADEUS W. GRABAU 



of Devonic affinities. This is further shown bv the occurrence of 

 Panenka and Hercynella in these beds. The highest division (Lucas) 

 is characterized by gastropods, most nearly related to late Siluric 

 types of northern Europe. 



The Amherstburg beds of the Upper Monroan appear to be the 

 chronologic equivalent of the Cobleskill of eastern New York, several 

 characteristic species being common to both. It represents the 

 junction of an eastern and a western sea, and a commingling of the 

 faunas of both. The typical Upper Monroan coral and brachiopod 

 fauna seems to have invaded Michigan from the northwest, a 

 somewhat similar fauna appearing near the headwaters of the 

 Saskatchewan. In Pennsylvania the Lewistown limestone appears 

 to represent this horizon. 



The Sylvania sandstone has all the characteristics of a wind- 

 drifted sand. Its cross-bedding is of the aeolian type, its grains well 

 rounded, pitted, grooved, and of uniform size; there is a total absence 

 of impurities, and all the characteristics compare favorably with 

 those of the sands of the Lybian desert of today. It indicates a period 

 of land condition between the retreat of the Atlantic embayment 

 (Lower Monroan) and the Pacific invasion of Upper Monroan time. 



G. THE LOWER DEVONIC 



The Lower Devonic comprises the Helderbergian and the Oris- 

 kanian of Clarke and Schuchert. The Helderbergian includes the 

 Coeymans, New Scotland, Becraft, and Port Ewen. The latter is 

 transitional to the Oriskany, and Chadwick proposes to unite it with 

 that formation.^ The Coeymans is the direct depositional successor 

 of the Manlius, there being frequently a transitional zone between 

 them, with a commingling of the fossils. The former extent of the 

 Coeymans can be estimated from its occurrence at Syracuse and the 

 uniform character which it maintains in that region. This indicates 

 that the western shore of the Helderberg sea was west of Syracuse 

 and perhaps in the region of Buffalo. The eastern and northern limit 

 of the formation is indicated by its mergence into shore deposits in 

 New Jersey, and the southward overlap of the later formations, 



I Science, N. S„ Vol. XXVIII, p. 347. 



