148 MINERALOGY AND LITHOLOGY. 
Hampshire was Prof. O. P. Hubbard, of Dartmouth college, who in 1837 
made a geological excursion through various parts of the state, and who 
made special observations on the eruptive dykes.* This gentleman rec- 
ognized clearly the great differences in these rocks, and noted the varia- 
tions in their appearance, even when situated side by side. But the 
means for careful discrimination being at that time beyond the reach of 
our science, all these rocks were classed together as trap. I hope that 
gentleman will not be displeased to know that some of his specimens, 
collected so long ago, have fallen into my hands, and that we now have 
the means for classifying them. 
Besides researches made on the rocks actually within our borders, 
more extended studies have been prosecuted on allied rocks in adjoining 
regions. The most prominent of the investigations are those prosecuted 
by Dr. T. Sterry Hunt, when connected with the Canadian survey.t The 
rocks which he studied and classified are nearly allied to ours, and in 
many cases identical. In reference to this work it may be said, that al- 
though microscopic study in many cases would, I think, cause a nomen- 
clature essentially different to be adopted, yet any new results which 
might by that means be attained would in no degree lessen the weight 
of Dr. Hunt’s reasoning in reference to the origin of this class of rocks, 
or any of his theoretical and geological conclusions, which must be what 
he chiefly values. The more essential features of Dr. Hunt’s work have 
been by him embodied in his Chemical and Geological Essays, a volume 
easily accessible to all, while the geological report is not. 
All our basic eruptive rocks are essentially compounds of triclinic feld- 
spar, with either hornblende or pyroxene, and, according to which of 
these latter minerals is present, they are divided into two classes. For 
the determination the microscope is often necessary, with the aid of 
which a number of accessory minerals are found, which are either essen- 
tial and constant, like magnetite and apatite, or accidental and variable, 
like chlorite, biotite, calcite, etc. The pyroxene or hornblende has at 
times been removed by process of alteration and decay; but still its orig- 
inal presence, and its influence in producing the structure observed, are 
so plain as to make no difference in the classification of the rock. The 
* Am. Four. Science, i, vol. xxxiv, p. 105. 
+ Geology of Canada, 1863. 
