PHYSICAL AND FAUNAL EVOLUTION 55 



sively higher beds appear beneath the quartzite in the direction 

 of the retreat, indicating continuous deposition during the slow 

 regressive movement of the sea, this being checked as the locaUties 

 successively emerged. 



A widespread negative diastrophic movement is thus shown to 

 have taken place over the whole of the North American continent, 

 accompanied and followed by the spread of subaerial elastics over 

 most of the area. At least 2,500 feet of calcareous strata were 

 deposited in the non-emerging areas, and most of this constitutes 

 the depositional equivalent of the retreatal movement (see map, 



Fig. 3)- 



The Beekmantown faunas. — The Beekmantown faunas are, so 

 far, best known from the Lake Champlain region, the Mingen 

 Islands, and the Newfoundland section. The Lake Champlain 

 region, including the PhiUipsburg section of the Canadian exten- 

 sion, has furnished a considerable number of species. Its distinctive 

 character will be seen on consulting pubHshed lists. 



The Pogonip limestone of Nevada contains mostly species un- 

 known outside of this formation in the West, though a number of 

 them have been referred by Walcott to eastern species, largely Tren- 

 ton and Chazy types. In almost all such cases, however, the identi- 

 fication is provisional, and regarded by Walcott himself as doubtful. 

 There is nothing in the character of the fauna which positively 

 demands its reference to either the Chazv or Trenton, as has been 

 done. 



GRAPTOLITE FACIES OF THE BEEKMANTOWNIAN 



In the Hudson and St. Lawrence valleys the Beekmantown is 

 represented by the lower portion of the Hudson River shales, above 

 the beds with Dictyonema jiahellijormis. Some 340 feet of strata 

 appears to be referable to this series, of which the lower 300 feet 

 constitutes the first and second Deepkill zones, synchronous with the 

 Upper Point Levis zone of Canada and the St. Anne zone of New- 

 foundland. Here the genera Chlonograptus, Goniograptus, Tetra- 

 graptus, and Phyllograptus (P. anna), with Didymograptns bifidus, 

 characterize a succession of zones recognizable in various parts of 

 the world. The upper forty feet of this series (third Deepkill zone) 



