Boston Meeting of the Geological Society. 213 
■its present state may stimulate further interest in the differentiation of 
ancient volcanic rocks from the other igneous and more or less meta- 
morphosed sedimentary formations with which they are associated in 
the crystalline belt of the Appalachian system. (This paperis published 
in full in The Journal of Geology, vol. n, pp. 1-31, with map, Jan.-Feb., 
1894.) 
35. Ancient eruptive rocks in the White Mountains. C. H. Hitch- 
cock, Hanover, N. H. In his report upon the Geology of New Hamp- 
shire, tbe author had described the granitic areas as built up of a series 
of eruptive rocks disposed much like sedimentary terranes. Resting 
upon a crystalline floor was the foundation called Conway granite, & 
coarse, well-defined, often reddish-colored granite, sometimes 1,000 feet 
; thick. It seems to lie in great sheets dipping slightly in anticlinal 
fashion. This is covered by the Albany granite, & porphyritic rock with 
abundant feldspar, disposed usually like the older underlying rock and 
sometimes fully as thick. It occurs also in large veins. Above this 
comes the Chocorua granite, or syenite, in which the feldspar is still 
more abundant. This is capped by porphyry; and that by a breccia of 
slate and porphyry fragments, to which the name of Pequawket breccia 
had been applied. The principle of this association had not been 
stated. 
The writings of Judd, Allport and other English geologists maintain 
that in Great Britain there is an association of granitic rocks similar to 
that just mentioned. In both areas one might climb a mountain, walk- 
ing successively upon the several granites, and finding the breccia at 
the top. Ben Nevis in Scotland is an illustration of these phenomena 
in Britain. The English authors regard these rocks as parts of one 
•great system of volcanic ejection. 
The same and other authors find a corresponding order of succession 
in modern volcanic rocks. At the base is a granitic core, and at the 
summit glassy and basic rocks. Owing to denudation, most of the 
glassy rocks would have disappeared from the Paleozoic volcanoes, 
but some of them might remain somewhat altered, as felsite and por- 
phyry. 
Professor Hitchcock stated that this principle explains perfectly the 
way in which these granitic rocks are associated in the White Moun- 
tains, and also makes unnecessary the dictum of Sorby that granites 
were formed at a depth of 40,000 feet. The whole series may be found 
in a vertical section of from 3,000 to 5,000 feet. Prom the summits of 
granitic cones like Mt. Ascutney and the Stratford peaks the higher 
rocks have been removed by erosion; but traces of them may remain, as 
the felsite upon the smaller adjacent cone of Little Ascutney. The ap- 
plication of this principle of association will be of the highest impor- 
tance in the understanding of our ancient granites. 
36. The chemical equivalence of crystalline ami sedimentary rocks. 
G. K. Gilbert, Washington, D. C. This paper gave the results of the 
combination of many analyses of the crystalline rocks and certain de- 
ductions therefrom concerning the totals of geologic erosion and depo- 
sition. Prof. F. W. Clarke took all the analyses of crystalline rocks that 
were available (in total 880) and combined them, after carefully study- 
ing their comparative value. (Bulletin No. 78, U. S. Geol. Survey, 1891, 
pp. 34-42.) His average of these analyses of the crystalline rocks is pre- 
sented in the following table of percentages: Oxygen, 47.3; silicon, 27.2; 
aluminium, 7.8; iron, 5.5; calcium, 3.8; magnesium, 2.7; potassium, 2.4; 
sodium, 2.4; total, 99 per cent. 
Mr. Gilbert then said that, assuming the sedimentary rocks to have 
been supplied by erosion from the crystallines, we obtain a method of 
■estimating how much sedimentary rock has been formed and the pro- 
portions of the different kinds. The aluminium was nearly all deposited 
