RANGE AND EXTENT. 519 



as some maintain, it almost necessarily follows that the force has essentially ceased to be 

 exerted after the production of the cleavage, that is, the foldings are all plicated before the 

 cleavage is produced. With all theories it is an admitted fact that it is produced after 

 the plication ; hence the folded beds in the above figure are strata, and cleavage is want, 

 ing. The same remarks apply to foliation. If this case is that of plication of strata, then 

 all the little undulations in the formation are the same, and we might remark stillYurther 

 that if the folded layers are strata, then the position we have adopted respecting the sedi- 

 mentary origin of these layers must be inferred. 



Secondly, the immense number of plications in the strata of talcose schist may enter 

 into our calculations respecting the thickness of the strata. Inasmuch as the problem of 

 the thickness of the formation is one of unusual difficulty to solve, every fact of the slight- 

 est consequence will contribute materially to the true result. If strata regarded as vertical 

 by all geologists in these metamorphic regions are as much divided into small convolu- 

 tions as the figure before us, at least one-half of the thickness calculated from observed 

 inclinations by trigonometry may be thrown away as excess. This shows us that a con- 

 siderable fraction of the whole may be disposed of, as this particular case may not occur 

 every rod. In disturbed regions fully one-fourth of the calculated thickness may be 

 safely left out of the" account. 



There is no unconformability between the talcose schist with the adjacent formations. 

 The succession is invariably unbroken. Rarely, however, there may be a very sudden 

 change in the position of the strata in the middle of the formation, as upon Sections X<z 

 and XI, in Hydepark and Wolcott, where there is nearly an abrupt change from vertical 

 strata to layers having a very small eastern inclination. 



Range, Extent and Thickness. 



As already intimated, there are three great ranges of talcose schist in Vermont. The 

 eastern, and smallest, lies partly in New Hampshire, along Connecticut River. It is the 

 most obscure of the three. It enters Vermont in Springfield, passes out again at the 

 Weathersfield " Bow," re-enters in the southeast part of Hartford, and continues in Ver- 

 mont until it terminates near Guildhall. The middle range, which is the largest, enters 

 Vermont from Massachusetts in the town of Halifax, and runs nearly north through the 

 State, greatly increasing in width near Plymouth, and passing out of Vermont into Cana- 

 da, in Troy and Newport. The western range, which is the widest of the three at its 

 northern part, is nearly of the form of a wedge, having its point in Bristol (possibly further 

 south), and being the widest at the Canada line, lying in the towns of Franklin, Berkshire 

 and Richford. The middle and western ranges unite north of Jay Peak. 



Commencing with the eastern range we will give a particular description of the rocks 

 of this group. 



North of Bellows Falls in Rockingham, there is an extensive surface between the ledges of 

 clay slate and the gneiss in which the ledges are obscured by alluvium. Inasmuch as fur- 

 ther to the north the talcose schist occupies a region between the slate and the gneiss or 

 granite, we might suppose that it would occur in Rockingham without any special evidence of 

 its presence. But in an excavation for the R. and B. R. R. just east of Rockingham Station, 

 there is a large ledge of a beautiful talcose schist dipping 60 W. The same rock occurs 

 again in the south part of Springfield along Connecticut River, and is exhibited in a more 



