Wadsworth.] 
258 
[October 19, 
state in which he found them. Of No. 168 (1389) Zirkel stated : 
“ The rock has no mica” (VI, p. 87), but the writer found mica 
in it. So, too, quartz was found in No. 187 (2723) although 
Zirkel says it contains no quartz. The hornblende in this rock 
is regarded by me as an alteration product. 
In the cases of the mica-diorites, Nos. 169 (1378), and 170 
(1380), it would seem as if some mistake had been made in the 
hand specimens, since they show but little trace of mica, and 
resemble some metamorphic schists. 
Hornblende Porphyry. 
.The specimens of hornblende porphyry, Nos. 189 (1435), 190 
(1418), are regarded by me as but little altered andesites which 
would never have been separated from the andesites if it had 
not been for theoretical views regarding their age. For Mr. 
Merrill’s benefit the writer would state that he does not believe 
in any “ ante-Tertiary precursor” of andesite, basalt, trachyte or 
rhyolite. What he means when he speaks of a rock being an 
altered andesite, basalt, etc., is that the rock originally was the 
same as andesites, basalts, etc. of the present day are ; and that 
the difference is in general owing to the alteration they have 
undergone since their consolidation. These altered rocks are 
sometimes old (Mesozoic, or older), sometimes not. As a rule, 
however, an old rock, especially if basic, is an altered one. The 
writer, agreeing with Professor Dana, denies that there is any 
valid lithological distinction between Tertiary and pre-Tertiary 
rocks, beyond this : other things being equal, the greater the age 
the greater the alteration. The writer holds that during the ear- 
lier geological ages basalts, andesites, rhyolites, etc., existed, which 
in their unaltered state were identical with those of the present 
day ; and that it is these rocks which, in their altered state, are 
now classed as diorites, melaphyrs, diabases, porphyries etc., etc. 
Diabase. 
Nos. 191 (750), 192 (754), 193 (761), 194 (764), 195 (773), I 
hold are altered andesites, containing much secondary quartz. 
Nos. 196 (520), 197 (532), 198 (533), and 199 (562), are taken by 
