POSITION AND EQUIVALENCY. 529 



Fig. 278 represents a specimen of a dendrite from the talcose schist in Newbury. It consists of small 



crystalline particles arranged by molecular forces in aborescent forms. 



_ FIG. 278. 



Geological Position, Equivalency, Origin and Metamorphism* 



Under clay slate we have stated, that judging from our 

 Sections across Vermont, we must infer, almost without ex- 

 ception, that talcose schist lies above clay slate, and is conse- 

 quently a newer rock. Moreover we have made it probable, 

 that some of the latter must be as new as the Devonian 

 period. True, our dips on the sections are those of cleavage 

 and foliation : but we have reason to think that those in 

 Vermont generally coincide with stratification, so that as the 

 evidence now stands, and leaving out the idea of inverted 

 dips, talcose schist is the newest of the Vermont rocks. 



Again, we have evidence in many places, that talcoid and even talcose schist may be 

 derived, by metamorphosis, from clay slate. All along the western part of Vermont and 

 of Massachusetts, our talcoid schist, which is the magnesian slate of Emmons, passes 

 insensibly into clay slate, and on the other hand into rock which cannot be distinguished 

 by external characters from the most genuine talcose schist ; and since the chemical 

 characters of this rock fail to identify it, we are obliged to rely wholly on its lithological 

 characters. Every geologist can easily recognize this rock in most cases, nor will he 

 doubt that it may be a result of a metamorphosis of clay slate. For it is not alone along 

 the western side of the State, that he witnesses the intermixtures of these rocks above 

 described, but also in the bands of clay slate along Connecticut River. Novaculite, such 

 as occurs in Guilford, is really nothing but a variety of talcose or talcoid schist. And 

 this on the other side becomes clay slate. So in Springfield we have seen the most 

 genuine talcose schist interfoliated with clay slate. 



If, as was formerly supposed, it was necessary to have a large amount of magnesia to 

 form talcose schist, we should not find it in clay slate. But it contains enough of this 

 ingredient to satisfy Mr. Barkers' analyses of the talcose schist, the talcoid slate, and the 

 novaculite of Vermont. The other ingredients could all have come from the clay slate. 



We do not maintain that all the talcose schist of Vermont is metamorphosed clay slate. 

 For we have shown how in some cases it has been derived from coarse conglomerate. A 

 considerable part of it, indeed, contains small pebbles, or grains mechanically rounded, 

 and no such rock could have come from slate. 



The changes which take place in talcose schist on the line of strike, are quite remarka- 

 ble ; but they will be more conveniently described under gneiss. 



The preceding theoretical conclusions are simply such as have been suggested by 

 looking at the rocks of Vermont alone. Very probably could we study those of Canada, 

 different results might have been reached. Indeed we believe the present opinion of 

 the Canada geologists is, that the talcose schist is the equivalent of the newly discovered 

 Quebec group. To such a view we have no objection, if sustained by adequate proof, 

 which we presume will be furnished when the results of the Canada Survey shall be made 



*By E. Hitchcock, Senior. 



