292 THE CAMBRIAN. [bull. 81. 



shale to the sandstone. The basal limestone is of Calciferous — Chazy- 

 Trentou age; the shales then would correspond to the Lorraine series, 

 and the sandstone to the Medina series of the New York section. As 

 as far known this is the only break in the continuity of the outcrops 

 of the u Granular Quartz," where a quartzite is present, from central 

 Vermont to Alabama. l 



At Rockfish Gap the massive chloritic argillites, that form the mass 

 of the Blue Ridge, are shown in unconformable contact with the lowest 

 Primordial strata. The Archean argillites are firm and hard, of a dark 

 greenish color, and present a strong contrast to the first stratum of the 

 Primordial rocks, the line of junction being strongly defined. Sum- 

 marized, Prof. Fontaine's description of the section is as follows, begin- 

 ning at the base: 2 



Feet. 



(1) Very thinly laminated slates oi shales 300 



(2) On the side next to (1), the layers of this rock in color, do not differ much 



from (1), but are thicker than the preceding slates, and more sandy. The 

 bedding thickens, and the amount of siliceous matter increases to the 

 west, until a fine-grained white kaolin sandstone is the result 75 



(3) Conglomerate of brownish-red color, in massive layers from 5 to 6 feet 



thick, with thin seams of shaly matter between several of the layers. 



The coarser materials are rounded grains of quartz of the size of a garden 



. pea and under ; inclosures of angular fragments of the slates of the Blue 



Ridge are not rare 60 



(4) This is a partially concealed interval of 200 feet in which the rocks are, 



when seen, kaolin shales and kaolin sandstone, principally the former. 

 To the west of this is a band of kaolin sandstone, with layers of cellular, 

 much indurated quartzite, and some subordinate beds of an indurated, 

 gray, coarse sandstone. This series contains one bed of the gray sand- 

 stone 20 feet thick. Thickness 420 feet or including the partly con- 

 cealed band 620 



(5) The first rock in this series is a highly indurated gray sandstone, the type 



of the beds above mentioned as forming occasional layers in No. (4). It 

 is of a dark gray color, and composed of coarse grains which by meta- 

 morphic action are changed to a nearly compact texture. The thick- 

 ness of the sandstone is 50 feet. A band of diorite 20 feet thick inter- 

 rupts the section, next to which is a band of bluish gray, coarse shales, 

 75 feet wide ; a partially concealed interval of 300 feet, occupied by 

 similar rocks: then for 200 feet, several alternations of the same shales 

 with bluish argillaceous sandstones. In these a layer 6 feet wide of red 

 argillaceous hematite is found. Then a second band of diorite 12 feet 

 wide, resembling in all respects the first. 

 (C) The beds of No. (5) which are mostly sandy shales, and are rather thickly- 

 bedded in layers of from 1 to several feet, are succeeded by a band of 

 very thinly-laminated, firm olive slates or shales, having a total thick- 

 ness of 300 



Indurated brown sandstone, with some chloi ite 30 



Interval of concealed rock 100 



Alternations of brownish argillaceous sandstones with greenish shaly beds. 150 

 Very finely fissile, pink-colored slaty shales, which weather purplish-red.. 200 

 Then for 100 feet a bluish shale is found 100 



880 

 >Bull. Geol. Soo. Am., vol. 2, 1891, pp. 155-163. »Am. Jour. Sci., 3d aer., vol. 9, 1875, pp. 416-421, 



