486 AGE AND POSITION. 



Connecticut valleys, indicating that they probably belong to different systems of uplift. 

 Is it not more probable that the clay slate once mantled over the strata intervening be- 

 tween these bands of that rock ? If so, erosion may have so cut down the middle of the folds 

 as not only to sweep away all the slate, mica schist, and metamorphic gneiss, but some- 

 times, also, to bring to light the hypozoic or Laurentian rocks. An examination of the 

 sections across Vermont will suggest the inquiry whether these lower rocks are not thus 

 brought to light there in some instances, as we have suggested in another place. Admit- 

 ting the probability of such an arrangement, we see the need of much further research 

 before we can pronounce with any confidence upon the age of the crystalline rocks of New 

 England, where they are not so connected with the fossiliferous that we can directly infer 

 a sequence. We confess, however, that the geologists of Canada have probably a better 

 opportunity for settling these questions than we have. 



In the south part of Derby we have found a section that may throw some light on the 

 age of the calciferous mica schist, as well as some other rocks. It is on the western border 

 of the schist, and much of it has that species of the mica family that has been described 

 as Adamsite ; nor have we noticed any limestone in it resembling that generally associated 

 with this schist. But the region is filled with granite which interpenetrates the schist, 

 and both rocks lie above, and are interstratified with fossiliferous limestone, probably the 

 Devonian. The sketch (Fig. 19) will give an idea of this example. The right hand side 

 extends nearly to the stage road from Brownington to Derby, and the first bed of lime- 

 stone at the foot of the hill is in an open field on the left hand side of the road, on the 

 farm of Mr. Robbins. The granite lies on the limestone very distinctly, even projecting 

 beyond it, as shown on Fig. 301 ; and the granite sends down veins into it in an interesting 

 manner. Above this granite we find another bed of mica schist, then another mass of 

 granite, then other beds of schist with limestone between them, then granite succeeds, 

 then slate, and so on over the whole hill, and even for at least two miles to Clyde River, 

 near its mouth. It is only the first four beds of granite, beginning at the right, that seem 

 distinctly interstratified with the schist and limestone ; for as we get nearer the top of the 

 hill, and so over its crest, the granite, so far as we could judge, seems thrust in more 

 irregularly among the schist, and it may be that all the granite beds are connected with, 

 or proceed from, the same mass of granite on the south side of the hill. But at the most 

 important point of the section the interstratification seems very distinct. The region 

 beyond the top of the first hill and to the Clyde, is covered mostly with woods, and all we 

 can say of it (for we only passed over it once) is, that we found frequently granite in 

 juxtaposition with schist, but often apparently in a very irregular position. Yet, near 

 the clay slate along the Clyde, the granite appears in great force ; but it has not much 

 disturbed the slate. 



Now, in the limestone underlying the granite in the above section, we found within a 

 foot or two of the granite a few encrinal stems, which unfortunately we lost. But the 

 geologist recognizes this rock as one that is fossiliferous further south in Vermont, and 

 also in Canada, especially at Owl's Head. The fossils there, as we have seen, are proba- 

 bly Devonian. If so, this granite and mica schist are of that age. Whether this would 

 bring the whole of the calciferous schist into that period we doubt ; for this spot appears 

 to be near the west border of the schist, and the dip of the strata is west as it would be 



