376 



Scientific Geology. 



rolled masses. Its peculiarity consists in the feldspar being compact,yet 

 exhibiting the form of the crystal. The feldspar is white and the schis- 

 tose structure of the rock distinct. (Nos. 948 to 950.) Whence this 

 rock originated I am unable to say ; though probably somewhere not 

 far from the outer limits of the granite range, which lies west of the 

 greenstone and sienite around Boston. It is quite obvious that this 

 rock must have been so nearly fused as to destroy the foliated struc- 

 ture of the feldspar, yet without essentially impairing its crystalline 

 form. 



3. Hornblende and Quartz. (Nos. 952 to 957.) In general this vari- 

 ety probably contains some feldspar also. The hornblende in a crys- 

 talline state forms the principal ingredient. The quartz is granular. 

 The rock is slaty ; and is sometimes traversed by veins of quartz or 

 granite. It does not form a common variety. 



4. Hornblende, Feldspar, and Mica. This approaches to gneiss : 

 but I do not call it gneiss, when the hornblende predominates. The 

 mica is usually in small quantity, and the feldspar and quartz some- 

 times traverse the rock in numerous minute veins, which seem to have 

 been frequently cut off and shifted by one another. (Nos. 958 to 963.) 



6. Hornblende and Epidote. This latter mineral sometimes con- 

 stitutes so large a proportion of the rock, that I thought it ought to 

 be regarded as a constituent of one of the varieties of Hornblende 

 slate. Generally it is granular and disseminated through the rock, 

 giving it a peculiar green tinge : but sometimes it is imperfectly crys- 

 talized in cavities, and sometimes in veins. (Nos. 964, 964 1-2, 965.) 



6. Hornblende and Chlorite. This variety is rather uncommon : 

 but I have met with it in Whately, Shelburne, and perhaps some 

 other places. Sometimes it passes into genuine chlorite slate. (No. 

 967.) 



7. Actynolite Slate. This is found in gneiss in Shutesbury ; and 

 I know of no other well marked locality. It occurs near the min- 

 eral well in the center of the town. The rock is slaty and is com- 

 posed of fibrous actynolite, foliated feldspar, mica, hornblende and 

 quartz, arranged somewhat in layers. It is obviously only gneiss 

 which takes into its composition a large proportion of actynolite. In 

 Belchertown I found a loose specimen, in which the actynolite was 

 granular and in large quantity, and the rock was not slaty. (Nos. 968 

 969.) Since the ablest mineralogists now regard actynolite and 

 hornblende as the same species, I can not see how Dr. Macculloch 

 can be justified in making a distinct rock of actynolite schist, as he 



