1881 .] 
259 
[Wadsworth 
me to be unaltered basalts, of which No. 197 is almost identical 
with No. 551 (565), (VI. p. 237), wdiile No. 199 has the same 
“ globulitic half glassy base ” as the basalt No. 551. All these num- 
bers (196, 197, 198, and 199) form with the basalts of Zirkel, Nos. 
551 (565) and 556 (689), a common series of rocks closely alike, 
and it seems to me they should never have been separated. 
No. 200 (1285) I regard as a diabase, identical with that 
described by me, as forming the edge of a large mass of diabase 
at the “Powder House” Somerville, Mass., the quartz in both 
cases being a product of alteration (Proc. Bost. Soc. Nat. Hist. 
1877, XIX, 281). 
No. 201 (1387) is a diabase almost identical with the rock form- 
ing the large dike at the “ Pumping Station ” Brighton, Mass. 
(1. c., p. 231). 
No. 202 (1680) can be regarded as a coarsely crystalized mela- 
phyr or a fine grained diabase, preferably the former ; while Col. 
No. 1704 (VI, p. 102) is a diabase. 
The terms melaphyr and diabase are used by me to indicate 
altered, and therefore generally old, basalts. 1 It may be said, once 
for all, that my criticisms against Zirkel’s species diabase, mela- 
phyr, etc., were made, because he uses the terms as indicating 
% 
species distinct from the rocks whose alteration forms I believe 
them to be ; therefore, as was proper, it was pointed out to what 
q>ecies they were supposed to belong to as varieties. 
Had Mr. Merrill used more care he would have seen that his 
criticism relating to diabase and olivine diabase, basalt, and aug- 
ite-andesite does not apply to work in which such mineralogical 
definitions of rocks are especially rejected ; but that it does 
apply to Zirkel’s work, since in his report he has given, without 
distinction between them, under diabase, basalt, and augite- 
andesite, rocks both “ olivine-bearing ” and “ olivine-free.” 
My statements regarding gabbro and diorite will be maintained 
in proper time and place ; but instead of confining myself to 
Mr. Merrill’s bald definitions, I shall try to show to what rocks 
these names have actually been applied. 
1 The use of these names is not advocated by me, but the present state of lithologi- 
cal science demands them, therefore I comply, but endeavor to show their relations to 
the unaltered rocks. 
