196 7. S. Hunt on the Crystalline Limestones of N. America. 
times dolomitic, and Hitchcock observes that in the granular 
marbles of Berkshire, pure and magnesian limestoues occasionally 
orm different layers in the same bed. (Geology of Massachu- 
setts, p. 84. 
In Orange county, according to Mather, it is easy to trace the 
transition from the unaltered blue and gray fossiliferous lime- 
stones of the Champlain division, (including the Calciferous sand- 
rock and the ‘T'renton,) to the highly erystalline white limestone 
with its characteristic minerals. (See his Report on the Geology 
of the first district of New York, pp. 465 and 486.) This view 
is fully sustained by H. D. Rogers in his description of the lime- 
Stones of Sussex Co., given in his final report on New Jersey, 
(cited by Mather as above, p. 468 et seq.) Mather farther con- 
cludes very justly that all the limestones of western Vermont, 
Massachusetts and Connecticut, and those between the latter state 
and the Hudson River, are in like manner altered Lower Silu- 
rian strata, (p. 464.) From the similarity of mineral characters, 
he moreover supposes that the crystalline limestones about Lake 
George are of the same age, and he extends this view to those 
of St. Lawrence County. Both of these however belong to the 
Laurentian series, and are distinguished by their want+of cou- 
formity with the Champlain division, and by their association 
with labradorite and hypersthene rocks which seem to be want- 
ing in the altered Silurian strata. The slates of this division in 
Kastern Canada, geuerally contain some magnesia, with very 
little lime, and four or five per cent. of alkalies, chiefly potash * 
hence the feldspar which has resulted from their metamorphosis 
is generally orthoclase, and they have yielded gneiss, and mica 
slate, which with quartz rock, and chloritic and talcose slates, 
make up the Green Mountains. 
* See my remarks On the Composition and Metamorphoses of some Sedimenta"y 
Rocks, Be Boor D, Philos, Magazine for April, 1854, p. 233, . 
