476 VARIETIES, 



* 



in Massachusetts, we are now able to make some addition. For it occurs more or less through nearly the 

 whole extent of Vermont, but in the northern part of the State it has a remarkable development. The 

 peculiar micaceous mineral above noticed increases in quantity until, as in the south part of Derby, it forms 

 most of the rock. It frequently, too, shows itself in distinct rhomboids, nearly half an inch long, and Prof. 

 C. U. Shepard, who regards it as an undescribed species, proposes for it the name of Adamsite, in honor of 

 the late Prof. Adams. But more of this under a subsequent head. We say here only, that the rock con- 

 taining it is made by it a distinct variety from the common mica schist. The characters of the mineral are 

 remarkably uniform throughout the 200 miles in extent where we have observed it. Whether it forms a 

 distinct species as a mineral or not, we think it characterizes a distinct variety of rock. 



7. Feldspathic. A small amount, but not much of feldspar, may enter into the composition of this 

 rock, and yet the characteristics of mica schist remain so prominent that we can hardly call the rock gneiss, 

 especially if the great mass of the formation be schist. Precisely where to draw the line, however, between 

 these rocks, when we admit the smallest quantity of feldspar to be present in mica schist, is no easy task. 

 And it has perplexed us exceedingly in regard to a large part of the rock in the Green Mountains. Though 

 feldspar be present in it, most of it has the aspect of mica schist ; and at first we were inclined to call it 

 feldspathic mica schist, as stated elsewhere. But other considerations have decided us to describe it as 

 gneiss. Yet in other parts of the State we have met with a few examples which we place under this variety 

 of feldspathic mica schist. 



8. Calciferous mica schist. This is the calcareo-mica slate of Professor Adams, and has been already 

 partially described. We prefer the name calciferous to calcareo-mica schist as being rather more appro- 

 priate and euphonical. For in general the basis of the rock is mica schist, which bears the limestone. On 

 the great belt of this rock, running through the whole State, the amount of the limestone increases as we 

 go northerly, and near the north end it is also purer and of a lighter color. Passing south into Massachu- 

 setts, the formation again expands, but the amount of calcareous matter is probably less. This rock has a 

 good many interesting relations, which will be noticed in the proper place. 



9. Conglomerate mica schist. This is uncommon, but sometimes met with. The pebbles are generally 

 quartz, and not large. The variety of schist in which we have noticed the conglomerate character most 

 distinctly is gneissoid, that is, a little feldspar is present. 



Beds and irregular masses of quartz are the most usual interstratified rock in this formation, though 

 granite sometimes forms beds in it. Other beds are clay slate, plumbaginous slate, hornblende, and talcose 

 schists and gneiss. There are dikes of trap and veins of granite and of copper. 



Divisional Planer. 



These are three : stratification, foliation, and joints. We have noticed no cases where the stratification 

 and schistose structure did not essentially coincide, though often one or the other was obscure, very proba- 

 bly because there was a discordance of this kind, which careful study might have traced out. 



STRIKE AND DIP. 



The following examples of the dip and strike of the calciferous mica schist have been measured : 



CALCIFEROUS MICA SCHIST. 



[The locality, strike and dip, and initials of the Observer are given.] 



Guilford (Algiers), strike N. 20 E., dip 55 E., C. H. H. Guilford, north part, strike N. 5 E., dip 75 E., C. B. A. 

 Guilford, north part, strike N. 12 E., dip 75 E., C. B. A. Guilford, strike N. 20 E., dip 85 E., C. H. H. Guilford, 

 strike N. 20 E., dip 55 E., C. H. H. Guilford, center, strike N. 20 E., dip 55 E., C. H. H. Guilford (Green Eiver 

 valley), strike N. 20 E., dip 25 W., C. H. H. Guilford, do., strike N. 20 E., dip 50 W., C. H. H. Halifax, east 

 part, strike about N. 20 E., dip 89 W., C. H. H. Halifax center, strike N. 45 E., dip 90, C. H. H. Brattleboro, 

 west of village, strike N. 28 E., dip 50 E., C. H. H. West Brattleboro, strike N. 10 E., dip 24 E., C. B. A. West 

 Brattleboro, strike N. 28 E., dip 67 E., C. H. H. West Brattleboro, strike N. 28 E., dip 38-45 W., C. H. H. West 



