W. M. Fontaine— Primordial Strata of Virginia. 427 
resembles that of the rocks of the “ White Mountain system.’ 
The structure of this belt, stated briefly, seems to be as lows 
ae lowest strata are certain heavily- bedded granitoid gneiss 
omposed of a little quartz, black mica, and the fe ape, 
albite and orthoclase. These show ee abundantly near 
Richmond and Petersburg. Passing to the west, these strata 
seem to be disposed in broad undulations, which sometimes 
bring them up through the overs schistose strata, especially 
along certain lines where true igneous eruptive ro ocks penetrate 
them. These massive beds are covered by a comparatively 
thin formation of typical gneisses and mica schists, abounding 
im quartz and mica. The overlying rocks are gneisses in the 
eastern portion of the belt and mica schists in the center, which 
become hornblendic toward the western edge. These schistose 
turbances. This entire ener is remarkable for the a 
motamorphign of the rocks, all the constituents being well seg- 
regated in large particles. 
Now if we compare the amount of metamorphism existing 
in the strata of the several belts, we shall find it increasing in 
a remarkable manner as we proceed from the Primordial, 
through the Middle, to the Eastern belt. 
I have already in this paper pointed out the difference in 
the amount of alteration shown in associated argillaceous and 
siliceous Primordial beds, and sented that I have seen nowhere 
in the Primordial belt the production over extensive areas of 
anything more than the first stages of metamorphism. It is 
true that certain strata exhibit a higher degree of ieee le but 
this is always due to intensified local action. If we pass from 
the lowest Primordial strata into those of the Middle belt, we 
note an abrupt change. The metamorphism of this belt is 
universal, but still not complete. The rocks are all crystalline, 
ut the ase epic De ticles are small, and the masses which 
they form show m or less want of cohesion. In the t in 
quartzites of the ack F ube of the Blue Ridge the texture is 
common, 
Am. Jour. Scr.—Tutrp — Vou. IX, No. 54—June, 1875. 
