WALCOTT.j SYNOPSIS. 369 



tion prevailed, and that great variation existed in what are considered 

 the same geographic provinces. The sediments of the northeastern 

 Atlantic Coast Province are almost entirely shales with a small propor- 

 tion of sandstone and a trace of limestone. Tracing the long Appa- 

 lachian Province from the Gulf of St. Lawrence to the southwest and 

 south, we find an immense accumulation of shale with some interbedded 

 sandstone and limestone. This extends to the Lake Champlain region 

 of New York and Vermont, where a great limestone of Lower Cambrian 

 age is subjacent to several thousand feet of shale in which lenticular 

 masses of sandstone and limestone occur at irregular intervals. Farther 

 to the southwest, iu southern Vermont and eastern New York, great 

 thicknesses of argillaceous sediment were deposited. These now form 

 the series of shales in which beds of finely laminated roofing slates 

 occur in massive strata. Toward the east, near the pre-Cambrian shore 

 line, the Lower Cambrian sandstones are followed by arenaceous, dolo- 

 mitic, and purely calcareous limestones of later Cambrian time. This 

 condition of sedimentation continues far to the south, varied more or 

 less by the presence of great thicknesses of shale above the lower 

 quartzite. Iu the latter case the limestone of the Cambrian forms only 

 a thin belt at the summit. 



In the Kocky Mountain Province the siliceous sediments, sandstones, 

 and quartzites are followed by limestone, and nearer the shore line, 

 the sandstones are subjacent to shale. Over the Interior Province the 

 record is sandstone, followed on the west and southwest by alternating 

 limestones and sandstones. 



On the map (PI. 11) the thickness and character of the sediment is 

 shown in a general manner for each of the provinces. 



The study of the fauna has shown that, while there is a general re- 

 semblance in the faunas of the Lower Cambrian in the Atlantic Coast, 

 Appalachian, and Rocky Mountain Provinces, there is sufficient differ- 

 entiation to mark off distinct faunal areas in the early Cambriau sea. 



The fauna of the Upper Cambrian is less specialized over great areas 

 than that of the Lower and Middle zones. The opportunities for com- 

 munication between the provinces were greater and it is only in the 

 Northeastern or the Atlantic Coast Province that a marked difference 

 is shown. 



The Middle Cambriau fauna of the Atlantic Coast Province is so 

 strongly differentiated from that of the Appalachian and Western 

 Kocky Mountain Provinces that it was not until they were found to oc- 

 cupy the same relative stratigraphic position that it was suspected they 

 lived in approximately the same epoch. 



The evidence of sedimentation and the evidence of organic remains 

 unite to prove that in Cambrian time the geographic and faunal prov- 

 inces were differentiated and established over the area of the present 

 North American continent. In fact, the sedimentation of the Cam- 

 brian was as varied as that of many of later geologic periods and more 

 so than that of the immediately succeeding Silurian (Ordovician). 

 Bull. 81 24 



