WALCOTT.] SYNOPSIS. 371 



Valley area of the Northern Appalachian Province the Lower Cambrian 

 and Upper Cambrian faunas are found in separate bands of conglomer- 

 ate limestones and not in situ, the great thickness of shales and sand- 

 stones referred to the Cambrian not being characterized by any known 

 fauna. In Vermont the Lower Cambrian fauna occurs throughout the 

 classical u Red sandrock n series and the lower portion of the super- 

 jacent Georgia shales, while about 2,000 feet above, the Upper Cam- 

 brian fauna is well determined. The Middle Cambrian fauna has not 

 been recognized. In the eastern New York section the Lower Cam- 

 brian fauna is strongly differentiated and the base of the Middle Cam- 

 brian fauna indicated; but the Upper Cambrian fauna is unknown. 

 Only a few miles distant to the west, however, at the base of the Adi- 

 r'ondacks, the Upper Cambrian fauna characterizes sandstones and 

 limestones that occur beneath the base of the Silurian (Ordoviciau). 

 Farther to the south, in Dutchess County, in the valley of the Hudson, 

 the Lower Cambrian fauna is recognized in the basal quartzite and the 

 superjacent limestone, and also the Middle Cambrian of the Appala- 

 chian and Rocky Mountain Provinces, and the Upper Cambrian of all 

 but the Atlantic Coast Province. In Tennessee, in the Southern Appa- 

 lachian Province, the Lower Cambrian fauna is found in shales, within 

 the quartzite series, and at the summit of the shales the Upper Cam- 

 brian fauna occurs. This extends up and into the base of the limestone. 

 In Alabama, in shales apparently occupying the same serial relation, 

 the Middle Cambrian fauna is well developed. 



In the Nevada section the Lower Cambrian or Olenellus zone is dis- 

 tinctly defined, and between it and the Upper Cambrian fauna 1,000 

 feet of limestone is marked by types of the Middle Cambrian fauna. 

 These distinctions of faunas are readily determined wherever two or 

 more of them are present in the same section in the Rocky Mountain 

 Province. In British Columbia the Lower Cambrian and Middle Cam- 

 brian faunas have alone been recognized. 



I have spoken of the Middle Cambrian fauna of the Atlantic Coast- 

 Province and that of the Middle Cambrian of the Appalachian and 

 Rocky Mountain Provinces. This distinction is made because the char- 

 acteristic types of the Atlantic Coast Middle Cambrian fauna are not 

 found in the Middle Cambrian fauna of the other two provinces. This 

 indicates that a nearly impassable barrier existed during Middle 

 Cambrian time between the sea of the Atlantic Coast Province and 

 those of the interior. This prevented nearly all the species of the 

 former from migrating into the Appalachian and Rocky Mountain Prov- 

 inces. Within the two latter there is a fauna characterized by similar 

 types in New York, Alabama, Nevada, and British Columbia, and in 

 each section where their stratigraphic position is determined they 

 occupy the same relations to the Lower and Upper Cambrian faunas 

 as does the Middle Cambrian or Paradoxides fauna of the Atlantic Coast 

 Province. 



