walcott.J SUMMARY VIRGINIA. 295 



with the nature of the adjoining Azoic. To the south they are more commonly com- 

 posed of gneissoid rock, but to the north the Huronian schists furnish the ma- 

 terial. * * * 



In the more southerly portions of the belt a good deal of partly decayed feldspar 

 may be detected in the finer matrix, but to the north argillaceous material forms 

 the cementing matter (p. 22). 



(2) Loiver Gray Shales and Flags. — The lower portion of this member of the Primor- 

 dial frequently contains bauds of conglomerate, composed of quartz pebbles, often 

 purplish in color, imbedded in a tine-grained matrix of shale or slate * * * 

 (p. 42). 



The lower gray shales and flags vary in character more than any other member of 

 the Primordial. The predominant rocks are shales, that sometimes become slaty in 

 firmness and thinness of lamination, or various more siliceous flaggy rocks that range 

 from purely argillaceous shales, through argillaceous sandstones, into massive and 

 highly siliceous quartzites. These latter have the character described above. The 

 predominant color is gray, but reddish, yellowish, or purplish and greenish colors 

 sometimes occur. 



Some of the grayish white, argillaceous strata form a species of claystoue that 

 weathers to a sort of kaolin. For the sake of distinction these may be called kaolin 

 flags. This kind of rock is much more common in the member next under the Pots- 

 dam quartzite. The conglomerates occurring in the lower part of this member have 

 been already described. 



The general features of the quartzite members of this group have been already suf- 

 ficiently discussed. Towards the southern portion of the belt, they attain great dimen- 

 sions. This is especially true of the space between tho southern border of Augusta 

 County and Balcony Falls. At this latter place a quartzite formation occurs about 

 150 feet above the base of the Primordial, forming the Balcony Rock. It lies in huge 

 beds of a highly siliceous character, and is not less than 250 feet thick. Here the 

 massive character of the beds has prevented the cracking and smashing, accompanied 

 with the infiltration of silica, so often seen in the smaller beds of qnartzite at this 

 horizon in other places ; otherwise the character is as given above for the lower 

 quartzites. I have never seen any casts of Scolithus borings in these quartzites. The 

 great quartzite at Balcony Falls disappears almost entirely in the northern portion 

 of the belt, its place being taken by minor beds of quartzite, and by shales and flags. 

 The subdivision of the Primordial beds now being described forms the lower portion 

 of the Primal older slates of the brothers Rogers. 



(3) lied Shales and Flags. — This also is quite a variable group, and it changes its 

 character very materially as we go south. In the northern portion of the belt, as far 

 as Mount Torrey, the greater portion of this group is composed of a tine-grained, 

 very thinly lamiuated, and tender slate. When fresh this rock has a steel gray color 

 and pearly or nacreous luster, but on weathering many portions become deep blood 

 red in color. Some of the lower and upper portions become yellow, but red is the 

 predominant color from weathering. Some bands have small pebbles of the size of 

 bird shot graduating iuto sand. Some of the red and yellow colors may be original 

 aud not due to weathering. This can not be decided, as all the exposures seen were 

 much weathered. This member, in its northern exposures, is often affected by faults 

 that cause it to extend over greater breadths than it could occupy in virtue of its 

 thickness. Quartz veins occur in it, having the nature of fissure veins. Bands of 

 this slate are impregnated with more or less specular iron, and this is the highest 

 member of the Primordial that shows iron in the specular form. Some greenish, 

 much indurated quartzite occurs in this member. This group to the south becomes 

 more siliceous and the amount of red coloring matter diminished. 



At Big Mary Creek the slaty character is nearly lost and the amount of red matter 

 is much less. The strata are now chiefly rather siliceous gray flags, and this charac- 

 ter is maintained to Balcony Falls ; there the rocks at this horizon are nearly all 



