358 TJie American Geologist. December, i899 
I. Feldspar in Jersey City Diabase — Ratio: 
RO:R203:Si02 i : i : 3-3 R.O : RO i. 4-7 
Labradorite. 
Hawes, G. W., op. cit., p. 131. 
II. Feldspar in Jersey City Diabase — Ratio: 
RO:R203:Si02 1:96:409 R2O : RO i. 2.2 
Andesite. 
Hawes, G. W., op. cit., p. 131. 
III. Feldspar in West Rock, Conn. Diabase — Anorthite. 
Hawes, G. W., op. cit., p. 131. 
IV. Feldspar from Dike 67, Trembleau Point, near Port Kent — 
Ratio: R2O : RO : R2O3 : SiOs i : f : 3 : 11 
Andesite. 
Kemp and Marsters, Bull. U. S. G. S., No. 107, p. 24. 
V. Feldspar in Olivine Diabase, Chatham, Virginia. Ratio: 
R3O : RO : RgOg : SiO^ = 1:2:3:11. 
Labradorite AbgAng 
Watson, Thos. L., Am. Geol. 1898, 22, 89. 
VI. Feldspar in Hypersthene Diabase, Culpepper Co., Va. — Ratio: 
R2O : RO : R2O3 : Si02 i : 5 : 6 : 17 
5 (Ca2Al4Si40i6) : 2(Na2Al2Si60i6) 5An : 2Ab 
Chemical properties indicate Labradorite. Optical properties point 
to Anorthite. 
Campbell and Brown, Bull. G. S. A., 1891, 2, p. 343. 
VII. Feldspar in Diabase, SE corner. Sec. 13, T. 47 N., R. 46 W., 
Michigan. 
Corresponding to Labradorite, with formula AbiAn2 
Si02 5i-347o AI2O3 31.20 7o CaO 13.67V0 Na20 3-79 7o 
Labradorite. 
Van Hise, C. R., Monograph, U. S. G. S., xix, p. 352. 
VIII. Feldspar in Diabase, Medford, Mass., according to Merrill 
and Hobbs is Labradorite and Orthoclase. 
Merrill, G. P., Bull. G. S. A., 1896, 7, 3So. 
Hobbs, W. H., Bull. Mus. Comp. Zoology, 1888, 16, No. "i. 
It is apparent from this tabular statement that the felds- 
pathic constituent in the normal diabase of the Atlantic border 
consists of the basic members of the plagioclase series, rang- 
ing from basic labradorite through andesite to anorthite, the 
most basic one of the feldspar group. When it is remembered 
that the basic members of the feldspar group yield niore readily 
to atmospheric agencies than do the more acid members of 
the series, the above point is significant as bearing on rock 
degeneration. 
The weathered product. The sample representing the de- 
cayed portion of rock was taken from the railroad cut about 
