GEORGIC PERIOD 517 



From the beginning of the Paleozoic, paleogeography can be made out 

 -with much certainty, but back of that period all is shrouded in obscurity, 

 -owing to the absence of a paleontologic record. On the basis of fossils, 

 there should not be the slightest hesitation in distinguishing between the 

 marine Paleozoic and Proterozoic rocks, and as a rule these are also easily 

 ■determined by angular unconformity. The late Proterozoic formations, 

 however, are very rarely fossiliferous, yet when organisms do occur, the 

 fauna is so inadequate and so different from that of the Olenellus period 

 •as to leave no question regarding its stratigraphic position. 



Over vast areas' of Canada, on both sides of Hudson bay, are found 

 •coarse fragmental deposits, often regarded as of Cambrian age, but latterly 

 Canadian geologists are inclined to pronounce these formations Protero- 

 zoic in time. All such unfossiliferous strata are eliminated from the 

 present maps. Sandstones and conglomerates of great thickness, and 

 containing no evidence of life, should be treated with considerable caution 

 when mapping them historically as marine deposits, for many such are 

 now turning out to be continental in character. For this reason, and 

 owing to the accumulation of many new facts since 1891, the late Georgic 

 map herewith presented differs essentially from the equivalent one pub- 

 lished by Walcott at the date mentioned. 



From the extent and position of the Lower Georgic invasion, it is in- 

 ferred that the North American continent was larger during the late 

 Proterozoic than at any subsequent period. 



The Georgic seas existed as synclinal seas along both sides of the 

 North American continent, the Atlantic waters being present in a long 

 but narrow trough to the northwest of Acadia and Appalachia. From 

 Labrador to Alabama the life represented is essentially that of the Ole- 

 nellus thompsoni fauna, though a knowledge of it has been acquired mainly 

 in Vermont and eastern New York. These facts were long ago pointed 

 -out by Walcott, who has ascertained most of what is known regarding the 

 American Cambrian. He also determined that these encroachments of 

 the Atlantic and Pacific did not occur along the continental platforms as 

 did those of Tertiary time, but that the Paleozoic was ushered in with 

 interior or continental seas, a fact that holds good throughout the Paleo- 

 zoic and for most of Mesozoic time. 



On the accompanying map, communication with the Atlantic has been 

 ■effected not only through the Saint Lawrence embayment, but also across 

 northern New Jersey. In the latter state, during the Paleozoic, the de- 

 posits in question are very frequently found quite near the ocean, and 

 when an Atlantic fauna is present in the strata of the Appalachian region, 

 as is often the case in later times, there can be no doubt that during the 

 •Georgic the Atlantic also entered the southern interior by this strait. 



