1881 .] 
243 
[Wadsworth. 
any distinct attempt to vindicate the original report — an under- 
taking as unnecessary as it would be presumptuous — it seemed 
highly desirable to call the attention of young American students 
in petrography to Mr. Wadsworth’s method before they shall have 
allowed themselves utterly to desert the testimony of those whom 
they have hitherto regarded as most qualified to speak. 
I will add that this examination of portions of the collection 
was undertaken by myself, at my own expense, purely for pur- 
poses of study, and that its results alone led me to write this 
paper in alliance with no one, and in defence of neither this nor 
that theory of the genesis of volcanic rocks. It gives me pleas- 
ure to acknowledge my obligation to the officers of the American 
Museum of Natural History, at New York, for the cordial hospi- 
tality extended to me while prosecuting my studies there, and 
especially to express my thanks to Mr. D. J. Mac Goldrick, of St. 
Francis Xavier’s College, who rendered me valuable help, and 
whose counsel in studying certain of the specimens I cannot es- 
teem too highly. 
SOME POINTS RELATING TO THE GEOLOGICAL EXPLOR- 
ATION OF THE FORTIETH PARALLEL. 
BY M. tS WADSWORTH, PH.D. 
Vr 
l^DIICTORY. 
Since the preceding pa^r Ms exclusively devoted to a criticism 
of an abstract 2 of mine published some over two years ago, it 
is necessary that some reply be made, on account of the impor- 
tance of the questions to American geology, and to lithological 
science. 
So far as Mr. Merrill’s paper goes it concerns the subject in two 
points of importance only : 
1. That the present writer had been mistaken in his use of the 
term “ original micro-felsitic base,” since the original use of the 
term was different : hence the present writer was unqualified for 
his work, and had made his statemqnts ignorantly. 
1 u Concerning the Lithological Collection of the Exploration of the Fortieth Paral- 
lel,” By Mr. N. F. Merrill. 
a Bull. Mus. Comp. Zool. 1879, V, 276-287. “ On the Classification of Rocks.” 
