500 AGE OF EOCKS. 



less of a crystalline aspect, and are less distinctly foliated, while the feldspars are hardly 

 developed at all, and ere long the clay slate and its associated limestones begin to exhibit 

 fossils. The rocks generally at the west of the synclinal line have a more earthy aspect 

 than to the east of it. 



Now it is along this synclinal that the chief development of quartz rock occurs, both in 

 Massachusetts and Vermont, and we might say the same of the belt of similar rocks 

 stretching southwesterly to Alabama. And if it occupy, as we have supposed, the bottom 

 of a synclinal trough, rising on the one hand uponUhe side of the Green Mountains, and 

 on the other upon the Taconic range, then it may be the newest of all the rocks of west- 

 ern Vermont. All agree that as we go eastward from Lake Champlain, for a time at 

 least, we pass over newer and newer rocks. But when we reach the crystalline limestone 

 and the quartz rock, which lie near the Green Mountains, it has been generally supposed 

 that these must be at least as old as the Potsdam sandstone. Our most recent discoveries, 

 however, have been leading us to the conclusion that these rocks are as high in the scale 

 as the upper Silurian, if not in the Devonian. Of the limestone, we have already 

 presented some suggestions ; but the only fossils hitherto found in the quartz rock, are 

 the Scolithus a supposed marine plant, and a species of Lingula. The former is 

 abundant in Bennington and Sunderland, as well as in Adams, in Massachusetts : but it 

 does not decide what the formation is. The latter, though found many years ago by 

 Henry Miles, of Monkton, has only in the autumn of 1860 been put into our hands, 

 by his kindness. Prof. James Hall has examined it, and says: "The Lingula, 

 though unsatisfactory, I regard as evidence of rocks of the age of the Clinton group of 

 New York, or of Medina sandstone a position reached by sandstones, a part of which 

 we include in the Clinton, and a part in the Medina sandstone." We incline to the 

 opinion that this main belt of quartz rock is at least as new as the Medina sandstone, 

 and should it turn out that the Eolian limestone is as new as the Devonian group, 

 possibly the quartz rock may also belong there. At any rate we have doubts whether 

 the old opinion, that it is as old as the Potsdam sandstone, can be maintained. 



On the supposition which makes the quartz rock and Eolian limestone very low in the 

 series, it was necessary to explain the facts to suppose faults to exist, and uplifts and 

 downthrows to have been made, where there is no evidence of such phenomena ; or if 

 these suppositions would not account for the facts, resort must be had to metamorphism. 

 By these means a geologist can prove anything he pleases in relation to the position of 

 rocks. But when he tells us that in such a place is a fault, or an uplift, or a downthrow, 

 we are not disposed to admit it without evidence, merely because it is necessary to 

 sustain his hypothesis. We have seen proof of such changes in the rocks of Vermont 

 in many places ; but our sections show that they have not all been inverted and dislocated. 



By reference to our description of the remarkable conglomerate of Wallingford and 

 Plymouth, and to our Sections, it will be seen that the quartz rock at Wallingford lies 

 above the conglomerate,- although the dip of both rocks is near 90. That conglomerate 

 we have been inclined, from its lithological characters, to refer to the Oneida conglomerate 

 or Shawangunk grit, of New York. This lies immediately below the Medina sandstone, 

 from the metamorphosis of which the quartz rock may have resulted. There can hardly 

 be any doubt that the conglomerate once mantled over the mountain, as represented on 



