Topography of Gneiss, 



385 



well as epidote. The latter mineral is very frequently in veins and 

 generally compact. It is sometimes, however, disseminated through 

 the rock, giving it a peculiar green tinge. Were this not a common 

 variety of gneiss, especially in the vicinity of hornblende slate, it 

 would not deserve a distinct description. It is closely allied to the 

 epidotic hornblende slate. (Nos. 1055 to 1061.) When the epidotic 

 gneiss happens to be porphyritic, it forms a beautiful ornamental stone. 

 (No. 1043.) 



7. Augitic Gneiss. This interesting rock is usually composed of 

 quartz, feldspar, and lively green augite, in coarse grains or partially 

 crystalline masses. Occasionally we see present grains of black 

 hornblende. The augite seems generally to have taken the place of 

 the mica. The augite is disseminated in various proportions through 

 the mass and the slaty structure is quite indistinct. (Nos. 1062 to 1065.) 



8. Anthophyllitic Gneiss. In the west part of Enfield and in Bel- 

 chertown, anthophyllite is disseminated through the gneiss in such 

 quantity, that it deserves to be considered an ingredient of the rock, 

 if it be proper thus to consider amphibole, epidote, and augite, in the 

 three preceding varieties. This rock is composed almost entirely of 

 feldspar, quartz, and anthophyllite, the mica being rarely present. 

 (Nos. 1066, 1067.) 



9. Arenaceous Gneiss. I have found this rock only in one well 

 marked locality, viz. at Southbridge, Worcester county ; but it seems 

 to me sufficiently peculiar to deserve a distinct notice. It is composed 

 entirely of quartz and feldspar, which, (particularly the latter,) are 

 in a finely granular slate ; embracing, however, small but distinct 

 crystals of red garnet. Between the layers of the rock we find a 

 substance which approaches to talc. This rock is quarried and is em- 

 ployed for lining furnaces. (No. 1068.) Perhaps it ought to be de- 

 scribed under the next variety. 



10. Talcose Gneiss. This is composed of feldspar, quartz, and 

 talc ; the first ingredient in the largest proportion. Its structure is ir- 

 regularly schistose : but it has the aspect of a rock formed in part by 

 mechanical agency. As I have met with it only in one place, (be- 

 tween Smithfield and Providence, R. I.) and did not there examine it 

 carefully, I am not prepared to say whether it ought to be regarded 

 as the Protogine of European geologists. (No. 1071.) 



Topography of the Gneiss. 



There are in Massachusetts four separate ranges of gneiss : one in 

 49 



