PRODUCTION OF SCHISTS. 39 



the cement of conglomerate, these agencies have formed mica, talc and feldspar, whose 

 parallel arrangement was probably the result, mainly, of pressure. We doubted for a 

 time whether we could justly include gneiss among the rocks that may have originated 

 from conglomerate ; for we have not found as yet, decided examples of pebbles in this 

 rock. Yet so intimately connected with the conglomerate schists is the Green Mountain 

 gneiss, as the preceding details show, so little in fact does it differ from the schists, that 

 we cannot doubt that both originated from the same original formation. But the conglom- 

 erate atWallingford affords still stronger evidence, and shows us the modes in which the 

 gneiss was produced from the conglomerate. Some of the elongated pebbles there are gneiss. 

 But we doubt whether they were originally so. For quite often the cement is changed to 

 gneiss. To effect this change it was only necessary that feldspar should be interpolated 

 between the folia of mica or talc. And no one who has seen the specimens will imagine 

 that it could have been introduced mechanically by deposition for example. The wet 

 way, or crystallization from solution, is the only other probable mode. Most likely gneiss 

 generally has been formed by such an interpolation of feldspar into the schists, and this 

 may be the reason why we seldom, perhaps never, see pebbles in that rock. We do not 

 yet despair, however, of finding pebbles in gneiss, now that we have learnt how to look for 

 them. Indeed some varieties of it contain nodular elongated masses of feldspar, interfo- 

 liated perhaps with mica, which may have been pebbles originally, which have been 

 changed chemically and elongated mechanically. 



The second agency by which conglomerate has been converted into schists, is mechanical. 

 By some force the pebbles have been flattened and elongated till they have become the quartz- 

 ose folia of the schists. It is not probably possible for us to convey a very clear and complete 

 idea of the evidence of this position. Would that our readers could, as we have done, 

 visit the localities again and again, and become familiar with the striking specimens there, 

 by repeated and careful examination. From our own experience, it would not surprise us 

 if the conversion of the pebbles of the conglomerates into the folia of schists should be 

 pronounced preposterous by able geologists. So the idea seemed to us at first, when the 

 facts forced it upon our attention. But as the facts compelled us to give up our scepticism, 

 so we think they will do with any candid mind. For if we look at almost any specimen 

 of the talcose conglomerate schist on the edge corresponding to the dip (Fig. 17), we 

 should see nothing but alternating folia of quartz and talc or mica, and pronounce it a good 

 example of the rock which we have called, and which is generally called, talcose schist. 

 But a fracture at right angles reveals the flattened pebbles (Fig. 17), and shows us that 

 their edges are what we have regarded as folia. Let the process of flattening be carried 

 a little farther, and no evidence will remain that they ever were pebbles. Who knows how 

 extensively the process may have been thus carried through in the schists and gneiss of the 

 Green Mountains, and how large a part of them may once have been conglomerates ? 

 Our aim, however, is not to show the extent of the metamorphosis, but only to prove its 

 occurrence on a large scale. 



4. A fourth conclusion forced upon us by the facts is, that the chemical constitution of 

 the pebbles has generally been altered in the process of metamorphism, without oblitera- 

 ting their original character as mechanically formed. 



As has been repeatedly stated, most of the pebbles in the Vermont rocks are quite pure 



