Geology and Mineralogy of a part of Massachusetts, &c. 9 
Associated with the mica-slate of the eastern part of this 
section are 
Trap or Hornblende Rocks. Cleaveland. 
This name, as is observed by Prof. Cleaveland, “ in fact 
conveys no definite idea of any one species or sort of rocks.’’* 
*Cleaveland’s Min. and Geol. 2d Ed. p. 743. There never was amore 
conclusive reason for discontinuing the use of n name. While some of the 
rocks are pure hornblende and others aggregates, the name does not even 
show the nature of the rock. A part of the rocks too, have no resemblance 
in their form, to that which led Werner tocail them trap rocks. In the in- 
dex to the Geology of the Northern States, p. 32 and 134, Hornblende Rock in- 
cludes only the primitive trap rocks, with sienite, which was not ranked with 
them by Werner, and excludes all the transition and secondary aggregates 
of hornblende and feldspar. Because of the similarity of the mgredients, 
however, the generic name will probably be continued. Much of the con- 
fusion attending this part of the science would be avoided by giving a tabu- 
lar view of the rocks comprised under the general term Trap Rocks, and 
by describing the several rocks in their order, under this generic name. 
To show the rocks of this section, I have put the account of the trap rocks 
in Rees’ Cyc. into a tabular form. See also Art. Mineralogy in the New 
Ed. Encye. for a similar view. 
TRAP OR HORNBLENDE ROCKS, 
Primitive Trap. 
1. Common hornblende, asa rock. 
Var. 1. Granular hornblende. 
2. Hornblende slate. 
2. Hornblende and Feldspar. 
Var. 1. Primitive Greenstone. 
Oe. Do. Greenstone Slate. 
3. Intimate mixture of hornblende and feldspar with some mica. 
Transition Trap Rocks. 
1. Transition Greenstone. aa cht Meta 
2. Do. Amygdaloid. , Known by their transition associates. 
Secondary Trap Rocks. 
1, Secondary greenstone, or greenstone trap. 
2. Basalt. 
3. Wacke, S&c. &e. 
Sientte must form another section, though no reason can be given, as it 
ig now defined, why it should not be ranked with the hornblende rocks. 
Vou. VIII. No.1. 2 
