386 THE CAMBRIAN. 



tULL. 81. 



deposits. It is only here and there that a deep-seated disturbance has 

 brought up the sediment that accumulated at some distance from the 

 shore line. In Vermont and Nevada, especially in the latter, the 

 calcareous sediments forming the limestone have been brought to the 

 surface. In the great interior area of Wiscousiu, Missouri, Texas, and 

 the eastern front of the Rocky Mountains and the northern line 

 between Canada and New York nothing is known of the deeper water 

 deposits, if any such existed. 



We know something of the sediments that accumulated along the 

 western shore line of the Appalachian protaxis; but what was de- 

 posited over the area of which Ohio, Indiana, Kentucky, Tennessee, 

 northwestern Alabama, Mississippi, northern Texas, Indian Territory, 

 Kansas, and Nebraska forms a part we know nothing. 



From the fact that in Texas, Missouri, the Upper Mississippi Valley, 

 along the eastern front of the Rocky Mountains, and in New York and 

 Canada west of the Adirondack's the deposits are such as would 

 accumulate in a shallow sea not far distant from the shore line it has 

 been assumed that the Cambrian ocean of this great area was rela- 

 tively shallow. I think that during Lower and Middle Cambrian times 

 the entire interior continental area was above the sea level. These 

 opinions are based on the character of the deposits and the absence of 

 the sediments of the Lower and Middle Cambrian. The great problem 

 in this connection, however, is to determine how far the pre-Cambrian 

 continent extended to the south and east and what its relations were 

 to the offshore ridges of the eastern and western margins, along which 

 we now find deposits of Lower and Middle Cambrian age. 



A careful study of the sections in Pennsylvania, Virginia, Tennessee, 

 Georgia, and Alabama may throw some light upon the question on 

 the southeastern side. Over the remaining portions of the great cen- 

 tral area no natural outcrops are known, and there seems to be no way 

 of obtaining information except by very deep borings. 



The question of the relations of the Middle Cambrian fauna of the 

 Atlantic Coast Province to that of the Appalachian and Rocky Moun- 

 tain Provinces is one that can be settled only by a close and careful 

 study of the faunas, based on large collections methodically made 

 throughout the entire areas of the three provinces. That the Middle 

 Cambrian or Paradoxides fauna of the Atlantic Coast Province is rep- 

 resented by a very different fauna in the Rocky Mountain Province 

 there is not, I think, any question. It is also well proved that the 

 latter fauna is present to a less extent in the Appalachian Province. 



Throughout the Rocky Mountain Province, except in British Colum- 

 bia, the Olenellus or Lower Cambrian fauna is confined to a very nar- 

 row zone, while in Vermont it ranges through 1,000 feet of limestone 

 and up into the superjacent shales. In New York it has a range through 

 a great thickness of shales, slates, interbedded limestones, and sand- 

 stones j and one of the problems requiring investigation is the downward 



