eT gr ene ee Se ee Ca er Ope Oe a eS a ee 
4nd silica present as impurity. 
J. D. Dana—Taconie Rocks and Stratigraphy. 448 
west of the emerging flats—how far west it extended it is not 
et safe to say ;—while to the east-and south there were, as I 
ave already explained, ‘solated areas of emerged or submerged 
rechean rocks, and, adjoining them, in some places, uncon- 
formably overlying sandstone (now quartzyte) which is proba- 
ly of Primordial age. 
e gradation in metamorphism does not vary with the 
amount of flexure in the beds, in this part of the Taconic 
region, but has depended on some more comprehensive action 
of this or some other cause. 
2. LIMESTONES. 
the limestone as an impurity. The limestone is carbonate of 
calcium and magnesium ; and tremolite and pyroxene are sili- 
cates (or rather bisilicates) of calcium and magnesium.* 
e gradation in metamorphism from north to south, which 
the preceding remarks have partly illustrated, I leave without 
review at this time, as the subject will be better explained after 
the facts relating to the rest of Berkshire have been presented. 
*In aper in this Journal for 1844 (xlvii, 135) and again in 1846 (II, ii, 88) I 
Point out the fact that the silicates, as well as phosphates, in crystallized lime- 
Stones may have derived their ingredients from the impurities of the original 
lies Sometimes from outside siliceous waters. In my Manual of Geology, edition 
of 1863 (the first) and later, I make the impurities of a limestone the source 
through metamorphism, of “i talline mineral h 
f * it 
article on the limestone of Westchester County in this Journal for 1880 (xx, 
i “ An Old Chapter of 
esian limest 
My opinion was then the same as stated in my Geology—that the hot silicate solu- 
tions were made within the limestone by the action of heat on the moisture 
