OEIGIN OF CRYSTALLIISTB ROCKS. 31 



with calcareous veius carrying the ordinary minerals of crystalline limestones, on the 

 other, is such that to all these veins must be assigned a common aqueous origin. It 

 was farther shown that the endogenous granitic masses or veinstones in the Montalban 

 or younger gueissic series in New England often attain breadths of sixty feet or more, and 

 that they present great varieties in texture, from coarse aggregates of banded orthoclase 

 and quartz, often with muscovite (from which these various elements are mined for com- 

 mercial purposes), to veins in which the concretionary character is not less marked, 

 including beryl, tourmaline, garnet, cassiterite and other rare minerals ; while others still 

 of these great veins are so fine-grained and homogeneous in character as to have been 

 quarried as granites for architectural uses. These endogenous masses are included alike 

 in the gneisses, the quartzites, the staurolitic mica-schists, and the indigenous crystalline 

 limestones of the Montalban series, and, though generally transverse, are sometimes, for 

 a portion of their coixrse, coincident with the bedding of the enclosing rock.'"* 



It was clear that these endogeuovis granitic veins of posterior origin were mineralogi- 

 cally very similar to the older gneisses and the erupted granites. From a prolonged study 

 of all these phenomena, the conclusion was then reached that we have in the action which 

 generated these endogenous granitic rocks a continuation of the same process which gave 

 rise to the older or fundamental granitoid gneisses, which were hence of aqueous origin. 



^ 61. This process of reasoning was in fact identical with that by which Werner, in 

 the last century, was led to assign an aqueous origin to the primitive granite and the 

 crystalline schists. In a farther description, in 18*74, of some examples of these banded 

 veinstones from Maine and Nova Scotia, it was said that their structure is " due to 

 successive deposits from water of crystalline matter on the walls of the vein, and results 

 from a process which, though operating in later times and in subterranean fissures, was 

 probably not very much unlike that which gaA^e rise to the indigenous granitic gneisses."'' 

 The same ideas as to the origin of the ancient crystalline rocks, and their relations to 

 granitic and to zeolitic veins, were farther defined by me, in 18*74, when it was said : 

 " The deposition of immense quantities alike of orthoclase, albite and oligoclase in 

 veins which are evidently of aqueous origin shows that conditions haA'e existed in which 

 the elements of these mineral species were abundant in solution. The relation between 

 these endogenous deposits and the great beds of orthoclase and triclinic feldspar-rocks is 

 similar to that between A'eins of calcite and of quartz, and beds of marble and of traver- 

 tine, of quartzite and of hornstone. But while the conditions in which these latter 

 mineral species are deposited from solution have been perpetuated to our own time, those 

 of the deposition of feldspars and many other species, whether in veins, or in beds, appear 

 to belong only to remote geological ages, and, at best, are represented in more recent times 

 only by the production of a few zeolitic minerals." '"' 



§ 62. A farther and more particularized statement of the author's conclusions as to the 

 origin of the crystalline rocks was embodied in a paper read before the American Associa- 

 tion for the Advancement of Science at Saratoga, in August, 1879, containing the three 

 following propositions : *' 



^* Amer. Jour. Science (3), vol. i., 88 and 182, and vol. iii., 115 ; also, Chem. and Geol. Essays, pp. 183-209. 

 ^Troc. Boston Society of Natural History, xvi. 237, p. 198. 

 ™ Chemical and Geological Essays, p. 298. 



*'The History of some Pre-Cambrian Rocks, etc. Proc. A. A. A. S., for 1879, and Amer. Jour. Science (1880) 

 xix., p. 270. 



