282 C. H. Hitchcock — Crystalline Rocks of Alabama. 



Within this Huronian synclinal, between the Green Mountains 

 and Connecticut River, lies a micaceous, argillaceous often 

 calcareous group, which is the latest formation in that section 

 of country. The east side of the Huronian synclinal is under- 

 laid by better characterized gneisses than those upon the west 

 side — and on reaching the watershed between the Connecticut 

 and Merrimack Rivers in New Hampshire we find the augen- 

 gneiss, which is regarded as the oldest rock in the north. 

 Between this ridge and the ocean there are several synclinals 

 filled with slates, quartzites or limestones of various descriptions. 

 The order in Alabama is the same, save that there is a pecu- 

 liar development of mica schist at several localities, particularly 

 in the White Mountains, and called Montalban in my writings, 

 which is not yet recognized, (d) Throughout the Atlantic 

 crystalline area the oldest of the gneisses lies from thirty to 

 fifty miles east of the Grreen Mountains and Blue Ridge range. 

 (e) Having had the opportunity to examine a copper vein in 

 Alabama, said to belong to the Ducktown type, I recognize the 

 familiar mineral character of the copper regions of Ely, Straf- 

 ford and Corinth in Vermont. The locality is the Woods 

 Mine, Cleburne County, fully described in Professor Smith's 

 report of progress for 1874. These veins occur quite near the 

 junction of hornblendic schists with mica schists. The iron 

 pyrites is the pyrrhotite. These veins are very different from 

 those of Lyman and Milan, N. H., and those near Lennoxville, 

 P. Q., which lack the pyrrhotite and are imbedded in the 

 Huronian. The Ducktown and Vermont copper regions were 

 of later origin than the others, and might be termed later 

 Huronian, corresponding to the Montalban of Dr. T. Sterry 

 Hunt. 



Final scheme of classification. — Perhaps for the present it may 

 not be needful to depart from the distinction laid down by 

 Logan in 1855 for the crystalline series, that of Laurentian and 

 Huronian. The beds commonly recognized as gneiss belong 

 to the former, while the chloritic, hydromicaceous and argilla- 

 ceous schists are chiefly Huronian. The latter are largely of 

 sediment derived from the pre-existing gneisses and granites. 



It has been necessary to speak of different sections of these 

 two great groups, and the terms upper and lower have been 

 employed. No term of geographical origin need be employed 

 to define the places of the several divisions. The Laurentian 

 of the east may be subdivided into lower, middle and upper or 

 the augen gneiss at the base, followed by well characterized 

 heavily bedded gneisses for the middle division, and coarse 

 mica schists or imperfect gneisses for the upper part. The 

 Lower Huronian would be the massive chloritic division, while 

 the upper part is more varied, being argillaceous, hydromica- 

 ceous, nacreous and quartzose. 



