BERKSHIRE OAS^ON 843 



of hills conspicuous from the surrounding country by their great variety of 

 brilliant colors. They are white, salmon-color, yellow, pale green, pale 

 lilac, gray, brown, olive, red, and deep purple, and present an equally 

 varied texture.. It is decidedly a massive outburst, and shows no tendency 

 to bedding, the various colors appearing as cloudings in one mass, and by 

 no means as a succession of ejections. In mineralogical composition, the 

 variation seems quite as well marked. Near the top of the hills, it forms a 

 pure white porcelainous rock of a fine microfelsitic groundmass, through 

 which wind translucent siliceous bands, shading off into the more homo- 

 geneous mass. There are large areas which show no inclosed crystals. 

 Following the same mass, either north or south, it is found to contain clear, 

 transparent grains of crystalline quartz, and some sanidin. Gradually the 

 sanidin and quartz crowd together, and make up nearly the entire material 

 of the rock, leaving but little space to be filled with felsitic groundmass 

 In such instances, the sanidin is largely decomposed, while the quartz, sur- 

 rounded by a thin coating of ferruginous material, has the color of garnet. 

 Much of the quartz occurs in irregular fragments, having no crystalline 

 boundaries, although in some a definite angle may occasionally be observed; 

 but there are no such crystals as characterize the green dacites. In a salmon- 

 colored rhyolite were noticed some large. cavities, in which were crystals of 

 carbonate of lime imbedded between coatings of siliceous sinter. Occa- 

 sionally can be noticed an appearance of fusion of the walls of the cavities, 

 resulting in an obsidian-like substance. Besides this, there occur, in the sal- 

 mon-colored rhyolites, passages of very fine, highly- siliceous, jasper-like 

 material. Decomposed sphaerulites abound, and it is not impossible that 

 these larger cavities may have resulted from the destruction of groups of 

 sphserulites, though they do not show the structure of lithophysse. Some 

 of the largest of these jasper masses reach 5 and fi inches in length, and 

 contain minute snow-white globules of apparently colorless jasper, scattered 

 irregularly through the red and green jasper bodies. The substitution of 

 carbonate of lime in the place of feldspars, noticed in the earlier volcanic 

 rocks, continues through the rhyolites. A few of the very clear and unde- 

 composed orthoclase crystals possess the "labradorizing" quality, and are 



