308 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



J. Arthur Phillips has continued his studies of the so- 

 called greenstones of Cornwall. The rocks thus distin- 

 guished by De la Beche include some masses which are in- 

 terstratilied with, and graduate into, the crystalline schists 

 of the region, and are believed by Phillips to be of sediment- 

 ary origin ; besides others which he conceives may have 

 been contemporaneous volcanic outbursts, which are, how- 

 ever, according to him, difficultly distinguished from the pre- 

 ceding; while others still are undoubtedly eruptive rocks in- 

 tersecting the strata. All of these are in their turn, how- 

 ever, traversed and displaced by intrusive granites. These 

 various greenstones, both coarse and fine grained, consist es- 

 sentially of a plagioclase feldspar, with augite or hornblende, 

 or of an association of these two, which, according to Phil- 

 lips, is probably the result of a partial transformation of au- 

 gite into hornblende, though in certain cases he conceives 

 that this latter may have been an original constituent. As- 

 sociated with these are viridite, occasionally with brown 

 mica, epidote, and apatite. These bedded greenstones, with 

 their associated crystalline schists, appear to have strong 

 resemblances to the rocks of the Huronian series, to which 

 further study will probably show them to belong. 



Von Cotta has lately defined his views on eruptive rocks, 

 the nature of which he maintains to be altogether indepen- 

 dent of the geological age or period of their eruption, both 

 acidic and basic ma<rmas having in all times either overflow- 

 ed or penetrated other formations, and having been accom- 

 panied by tufas. When consolidated at great depths, these 

 magmas constitute plutonic rocks; but when nearer the sur- 

 face, volcanic rocks. Thus the acidic materials give rise 

 either to granites and porphy rites, or to trachytes and tra- 

 chytic lavas; and the basic materials to diorites and green- 

 stones, or to basalts and basaltic lavas, according to the con- 

 ditions of their solidification. 



Similar views have also been insisted upon by Hunt, who 

 remarks that inasmuch as the more ancient neptunian for- 

 mations, with their accompanying eruptive masses, have in 

 most cases been subjected to great erosion, it results that 

 the superior or volcanic portions of the latter have generally 

 disappeared, the inferior or plutonic portions only remain- 

 ing. Hence it has come to pass that granites and green- 



