160 Scientific Intelligence. 



relations of diorytes and other " greenstones." The rocks which 

 it describes are greenish slates, greenish crystalline rocks without 

 a trace of lamination, into which the slates pass by gradual or 

 abrupt transitions, and also killas or clay-slate. The kinds of 

 greenstone least metamorphic consist, as seen in thin sections 

 under the microscope, of a plagioclase feldspar, augite or diallage, 

 magnetic titanic iron, with occasional specks of pyrite, and also a 

 little apatite, and with rarely flakes of brown mica, some horn- 

 blende, and a chlorite. The more altered kinds have a semi- 

 transparent base, through which hornblende and the chlorite are 

 thickly disseminated; and in it there are green pseudomorphs 

 ' j, and faint outlines of feldspar crystals. In some placer 

 lara-e crystals of the feldspar, yet with the augite 

 dende and chlorite. The material of the inter- 

 secting veins is the same, except that it contains a little more 

 green hornblende. In other places the augite is but slightly 

 altered, while the feldspar crystals appear merged in a colorless 

 slightly opaque base, which shows faintly the outlines of the feld 



Four different varieties of the greenstones afforded on analysis: 



No. 1 is greenish and crystalline, and consists, as shown micro- 

 scopically, mainly of augite and feldspar, the former predomi- 

 nating, with some chlorite, brown and green hornblende, and 

 magnetite; and came from north of St. Peter's Vicarage in Tol- 

 carn. No. 2, from Tolcarn Quarry, resembles No. 1, but is of 

 lighter color, and consists of feldspar with altered augite, chlorite. 

 magnetite partly replaced bv a greenish-grav mineral, and apatite. 

 No. 3, from Tofcarn Quarry, is \ cry tine-grained crystalline, sage- 

 green in color, and consists chiefly of hornblende and altered 

 feldspar and chlorite, the augite being replaced by hornMende 

 and chlorite. No. 4, from Chapel Rock ("which rests on slate"), 

 is crystalline and greenish-gray, somewhat felsytic in appearance 

 and consists of a feldspar base, with crystals of feldspar, hornblende 

 : . . chlorite, apatite, magnetite. 



With these rocks occur fine-grain crystalline slaty kinds, which 



