Geology and Mineralogy. 231 
the: grains offered no peculiarities to conflict with the above de- 
termination. 
his method of rave as Dr. Hawes is aware, has a source 
of error in the fact that the grains of a fine-grained crystalline 
rock will not ahogether, and pets not generally, be wholly free 
from admixture, owing to the adhesion and interpenetration of the 
blended; hence, while the existence of at least two feldspars is 
thus plainly proved, the analyses of the two parts can give only 
Sep emate results, and so they are regarded by the author. 
There is another source of uncertainty as regards ie feldspars 
of such a oie in the similarity of specific gravity of some of the 
species. The range for the ies minent kinds, excluding some ex- 
treme numbers, are as follow 
Orthoclase _.... 2°60—2°59 Andesite. -.--. *65—2°7T2 
Bos! cae 2°59—2°63 Labradorite -. .. nt 66—2°72 
Oligoclase.. .._- a an Anorthite _. _-.. 2°70—2-77 
Anorthite from all its localities (with a rare exception), about 
half of the varieties of Labrado ie: pe one-third of those of an- 
desite, have the specific gravity 2°69 or above; the rest, below 
2 The vais that are thus Hiatt chemical analysis can 
in anit remov 
awes colin as follows: “The ee be of the anor- 
thite and augite that I picked from West Rock may be added, 
and our knowledge of this diabase may be said to be quite com- 
plete as regards the composition of the fresh rock. I will place 
ae pe analyses of the rock and its other components. Pro- 
"The te analyses are then cited from the article by him 
just referred to :+ 
SiO. Al.Os Fe,0, FeO MnO MgO CaO 
West Rock, New Haven.. 51°78 12°79 3.59 825 0-44 1763 10°70 
Augite, West Rock... _. 50°71 355  — 15°30 0°81 13.63 13°35 
Anorthite, West Rock ... 45°95 3470 O84 — 1830 w. 15°82 
Na,O0 K.O TiO, P.O; Ign. 
est Rock. New Haven.. 2°14 0°39 1°41 O14 -063 = 99°89 
serge West Rock... .. (48). oS ee COT = ONO 
Ano northite, ‘West Ro ck 2. 0-45 ee — 096 = 10032 
* This Journal, ix, 183, 1875. 
i* 44 ae ne analysis of oo from his former paper, several changes 
ei 45 MnO instead of CaO, evidently by a slip of the 
on and this is corrected teas ; but, further, 1°80 is opposite MgO, when it 
7 7 amount of K,O in the original ae and 0 Sate 8 put io fea and 
i 1 
