Merrill.] 
466 
[April 5, 
that a rock showing macroscopically abundant quartz, abundant 
mica and considerable hornblende, and not even carrying olivine, 
like No. 323, would not be pronounced macroscopically a basalt ; 
yet such is Mr. Wadsworth’s finding. 
Another of these, No. 332, shows macroscopically very much 
mica in quite large plates and under the microscope I found the 
feldspars to be almost wholly sanidin. Such a rock would not 
generally, by most lithologists, be thought to resemble a basalt. 
It is, however, a curious specimen, carrying decomposing olivines 
and fresh augites. Nos. 325, 327, 332, are the only ones of these 
seven rocks now under discussion which carry olivine. All but 
one or two of them carry quartz. 
These quartzes are all strikingly alike, — greasy in lustre, broken 
and cracked in structure. They jirobably have all lived through 
the same experience, whatever that may have been. Now, the 
thin section to No. 323, one of these Elkhead rocks, shows one of 
these quartzes which carries glass inclusions and inclusions of 
what seems undoubtedly to be the groundmass of the main rock. 
Moreover, besides this, occasionally there is found one of the 
augitic microlites precisely similar to those forming the border 
around the quartzes described by Zirkel, included within the 
quartz. Several of these quartzes carry inclusions of the half- 
globulitic base occurring in the main rock. Therefore, I do not 
think that the quartzes in the Elkhead specimens are foreign 
to the rock in which they occur, as Mr. Wadsworth asserts, but 
that they separated out from the magma of the rock. 
Of these specimens No. 327 most resembles a basalt, macroscop- 
ically and microscopically, it seemed to me, and does somewhat 
resemble the basalt No. 612 1 of the Report as Zirkel mentioned 
(Report, p. 161). Zirkel has said (Report, p. 251) that this spec- 
imen, No. 612, carries no olivine, and Mr. Wadsworth says that 
that mineral may be seen in the thin section in considerable quan- 
tity. 2 I do not think that the section shows olivine. 
Concerning specimen No. 326, Mr. Wadsworth writes: “The 
slide No. 326 (2614) is not believed by me to have come from the 
rock with the label Col. No. 2614.” 3 
1 This is erroneously given as No. 328 in Repoi’t, p. 161. 
2 These Proceedings, Vol. xxi, p. 266. 
3 These Proceedings, Vol. xxi, p. 267. 
