OEIGIN. 421 



crowded into successive folds, the remnants of which we still find in the anticlinal and 

 synclinal axes not uncommon. As we go west the strata show less of plication. 

 The horizontal position of the strata on Eolus, Equinox, &c., may be the top or bottom of 

 the folded axes ; though we can easily believe that the enormous lateral pressure which 

 seems to have been exerted along the west side of the Green Mountains, may have lifted 

 up the strata bodily, to a great height. 



But where among the palaeozoic rocks shall we find such a thickness of limestone, and 

 of slate, capable of becoming talcoid, as occur in these mountains ? Nowhere unless it be 

 in the lower Silurian, or the carboniferous groups. The Professors Rogers make their 

 Auroral magnesian limestone (the equivalent of the Chazy limestone of New York) 

 2500 feet thick in Pennsylvania, and the Matinal argillaceous limestone immediately 

 above the Auroral, 550 feet, succeeded by black slate and shale some 1600 feet thick, 

 which might by metamorphosis be converted into talcoid schist. But there are great 

 difficulties in making these rocks as old as the lower Silurian. 1. We have already shown 

 that along the west margin of the fossiliferous rocks, say at Whitehall, we find the older 

 Silurian rocks lying upon the gneiss in undisturbed position, and succeeding one another 

 regularly, as we go east, as high certainly as the Hudson River group. Most of the 

 talcoid schists and the Eolian limestone lie apparently above all these, and though they 

 have been a good deal disturbed, yet how to bring them into the lower part of the 

 lower Silurian we know not, without supposing the most improbable vertical 

 movements along the lines of undiscovered faults, and total inversions of the strata. 

 2. A still stronger difficulty lies in the facts we have discovered, in respect to organic 

 remains. As detailed above, we have found, mostly in strata below the middle of the 

 limestone, fossils, which, though obscure from metamorphism, are clearly referable to 

 genera characteristic of Devonian rocks, viz., the Euomphalus, Stromatopora, Zaphren- 

 tis, Chsetetes, and encrinal stems. The limestone in which they occur, exceedingly 

 resembles that from Memphremagog, which contains other fossils of a decidedly upper 

 Silurian or Devonian type. 



But neither in the upper Silurian nor the Devonian, as they have been explored in 

 other States, do we find limestones of sufficient thickness to have produced the Eolian. 

 But in the carboniferous rocks, above the Devonian, the Umbral series of the Professors 

 Rogers, we find a thickness of 300 feet assigned to red shales and limestone. Nor is 

 there any improbability, as we shall shortly show, in supposing that Eolian limestone may 

 be as recent as the carboniferous rocks. We incline to the opinion that they must 

 probably be placed as high as that formation, or as low as the lower Silurian : to which 

 last position Mr. S. T. Hunt assigns them. Either supposition abounds with difficulties, 

 and we are hardly prepared to choose between them. We have already stated the views 

 of Prof. Emmons as to this limestone. The fossils seem to be the greatest objection to 

 them. 



The metamorphism is generally accomplished in the wet way, that is, water is the prin- 

 cipal agent. Where the metamorphism has been most thorough, we have reason to sup- 

 pose the water to have been hot, and that the whole has been brought into a plastic state, 

 so as to allow of the introduction and abstraction of foreign ingredients. A striking 

 evidence of this plastic condition is seen in the Winooski marble, which is a silicious 



