PHYSICAL AND FAUNAL EVOLUTION 63 



chronous with the shale, carry a Lowville-Black River-Lower 

 Trenton fauna, with some elements {Christiania trentonensis, Ampyx 

 haslatus, Remopleurides, Sphaerocoryphe, Cybele, etc.) suggesting 

 a geographic connection with the European sea of that time. The 

 typical graptolite fauna of the Normanskill includes more than 60 

 species in all, though the widely distributed forms are much fewer. 

 The more constant and characteristic species comprise: (i) Coeno- 

 graptus {Nemagraptus) gracilis; (2) Dicellograptus sextans; (3) D. 

 divaricatus; (4) Dicranograptus furcatus; (5) D. ramosus; (6) Diplo- 

 graptus joliaceous; (7) D. angustijolius; (8) Climacograptus parvus; 

 and (9) C. hicornis. Of this list, Nos. i, 2, 4, and 8 are the most 

 characteristic index fossils of this zone. Didymograptus sagitticaulis, 

 Gurley, and Climacograptus scharenbergii, Lapw, may also be men- 

 tioned as characteristic though less widely distributed forms. 



Besides the numerous localities along the Hudson and St. Law- 

 rence valleys, this fauna is known from Maine and New Brunswick. 

 In the Appalachian region it is definitely known only from New 

 Jersey and from Bebb County, Alabama; it is also doubtfully identi- 

 fied from western Virginia and eastern Tennessee. It has been found 

 in Arkansas and the Ouachita Mountains of Oklahoma; in southern 

 Nevada (Belmont and Letson peak) ; and in the Kicking Horse Pass 

 of the Rocky Mountains of British Columbia. It is also known from 

 New South Wales and Victoria in Australia; and from southern 

 Scotland, Scania, and France. 



The distribution of this fauna is such as to suggest an eastern 

 and a western land mass (Appalachia and Rockymontana) of low relief, 

 with currents of the Gulf Stream type sweeping along their inner 

 borders and distributing the graptolites, which became entombed 

 in the muds that accumulated in these channels of moderate depth. 

 The division of what was probably a single great current, sweeping 

 north along the South American coast, and carrying the graptolites 

 from Australia, was probably due to the existence of an Ozarkian 

 island or Archipelago, along the borders of which, as in Arkansas 

 and Oklahoma, were deposited some of these black muds. One arm 

 of the divided current swept along the east coast of Rockymontana 

 to the Arctic Sea of Alaska; the other along the west coast of Appa- 

 lachia, past a Newfoundland island, and across the North Atlantic 



