Merrill.] 
240 
[October 19, 
unaltered ones, the remainder being altered old andesites.” Now, 
on page 279 Mr. Wadsworth when speaking for himself states 
that the coarser grained basalts through their alteration give rise 
to the diabases. The question then arises : If basalts by alteration 
form diabase, why criticise any of Zirkel’s diabases because they 
are found to be such altered basalts? Again, he says : “ The mel- 
aphyrs [of Zirkel’s report] are all old, altered basalts, except one, 
which is an old andesite.” But, on page 279, Mr. Wadsworth 
has said: “the fine-grained, compact basalts through their altera- 
tion give rise to the variety known as melaphyr.” Why, then, 
complain of any of Zirkel’s melaphyrs for being “old, altered 
basalts”? Does it not appear, then, either that Mr. Wadsworth 
uses the terms : “ old, altered ” confusedly, or else that his com- 
plaints are inconsistent with his own declared principles ? To 
return to the hornblende-porphyries in question, if the expression : 
“ somewhat altered andesites ” means the pre-tertiary equivalents 
or forerunners of hornblende-andesite, that is precisely what true 
hornblende porphyries are, and I think, from my own study of 
these two specimens, that that is just what most students, who 
afford themselves the pleasure of a visit to the museum, will find 
them to be. From the above quotations it will be seen that 
all of Zirkel’s diabases and all of the melaphyrs are disposed 
of just as the diorites were. Twelve diabases and seven mela- 
phyrs are mentioned in Zirkel’s report. Here, again, my own 
study of these rocks rendered Mr. Wadsworth’s statements, as 
they stand, incomprehensible to me. I may say that it is perfect- 
ly true that a few of the specimens pronounced in the report to 
be diabases I should at once regard as basalts 1 were I to depend 
1 The specimen described under number 198 of the printed report, but which bore the 
collection number 533 when I saw it, furnishes such a case. Number 199 of the printed 
report (562 “ coll, number ”) is another instance, so far as the microscopic analysis 
alone is concerned. Specimen number 200 of the printed report (1285 “coll, num- 
ber” ) is, indeed, as Professor Zirkel has stated, suggestive of a tertiary dolerite. I 
carefully compared this thin section with one of a dolerite from Port Rush, Ireland, 
from my own collection, and the similarity was striking in several points. A very 
marked distinction was, of course, the presence of quartz in the diabase and its ab- 
sence in the Port Rush dolerite. In one of these quartzes may be seen a remarkably 
beautiful fluid inclusion with a very large bubble moving majestically about. This 
fluidal inclusion measured about .009 mm. to .01 mm. in length, by .004 mm. in 
breadth ; its beauty was remindful of some of the inclusions of liquid carbonic anhy- 
dride of the famous Brazilian topazes. 
