Tlie Position of the Cincinnati Group. 101 



of the rocks. He subdivided it into the Lower Silurian and Upper 

 Sihirian formations, and those names have been adopted in this coun- 

 try almost without exception. The Lower Silurian is divided nito 

 groups or subdivisions in ascending order, as follows : 



1st. The St. John's Group, consisting of black shales and sandstones, 

 resting conformably upon still older schistose rocks, at St. John's, New 

 Brunswick, 3,000 feet thick. (Geo. of Can., 1866, p. 235.) 



2d. The Potsdam sandstone, which takes its name from Potsdam, m 

 Northern New York, where it is well developed, and consists of a fine- 

 grained, even-bedded sandstone, traversed by parallel vertical jomts. 

 It is about 2,000 feet thick in Pennsylvania and West Virginia, 1,147 

 feet at the Straits of Belle L^le, 2,020 feet at Bonne Bay, Newfound- 

 land, and from 500 to 2,500 feet in thickness at other places in Canada. 

 It is divided into three great sub-groups in Tennessee, in ascending or- 

 der, as follows : 1. Ocoee conglomerate and slates; 2. Chilhowee sand- 

 stone ; 3. Knox Group. The Ocoee conglomerate and slates takes 

 its name from the Ocoee River, and is 10,000 feet in thickness. The 

 Chilhowee sandstone takes its name from the Chilhowee Mountain,^ and 

 is 2,000 feet thick. The Knox Group takes its name from Knox 

 couiitv, and is 7,000 feet in thickness ; thus making the total thick- 

 ness of the Potsdam 19,000 feet in Tennessee. (Safford's Geo. of 



Tenn., p. 158.) 



3d. The Calciferous Group, which is exposed in Illinois, Missouri, 

 Tennessee, New York, Pennsylvania, Canada, and other places, usual- 

 ly less than 500 feet in thickness, is 1,315 feet thick in Missouri. (Geo. 

 of Mo., pp. 60, 116), and 1,839 feet in Newfoundland. (Billing's Pal., 



p. 208.) 



4th. The Quebec Group, which is subdivided into the Levis, Lauzon 

 and Sillery. The Levis division comprehends the Philipsburgh rocks, 

 which are 4,860 feet thick, in addition to 1,285 feet of the Orleans 

 section, making the whole division 6,145 feet thick. The Lauzon di- 

 vision reaches nearly 4,000 feet in thickness, and the Sillery 2,000 

 feet, making the maximum depth of the three divisions of this group 

 12,145 feet. (Geo. of Can., 1866, pp. 30, 36.) Some of the fossils of 

 this group are found in both the Chazy and Calciferous rocks, and the 

 Canadian geologists for a time supposed it to be the equivalent of 

 these rocks, but later investigations have shown that it has a fauna of 

 its own, and that it offers beds of passage from the Potsdam to the 

 Trenton founa, in addition to those of the Chazy and Calciferous. 

 (Billing's Pal., p. 64.) 



There is in Newfoundland an important series of strata, having a 

 thickness of 2,061 feet, lying below the Levis formation, and above the 



