OEIGIN OP CRYSTALLINE ROOKS. 33 



§ 68. The transformation of the primary basic layer, judging from the phenomena 

 seen in basic exoplutouic rocks, would give rise not only to qnartz, feldspars and zeolites, 

 but to aluminous silicates like epidote, chlorastrolite and prehuite, and to uon-alvTminous 

 silicates like pectolite, okenite and apophyllite. These silicates are all uon-maguesian, 

 but their reactions, while in a soluble condition, with dissolved magnesian salts would 

 give rise to various natural magnesian silicates, both aluminous and non-aluminous. 



§ 69. The cooling of the surface of the earth by radiation, and the heating fi-om 

 below, would establish in the disintegrated, porous and unstratified mass of the primary 

 layer a system of aqueous circulation, by which the waters penetrating this permeable 

 layer would be returned again to the surface as thermal springs, charged with various 

 matters there to be deposited. The result of this process of upward lixiviation of the mass 

 would be the gradual separation of the primary undifferentiated layer into an upper 

 stratum, consisting chiefly of acidic silicates, such as feldspars with quartz, and a lower, 

 more basic and insoluble residual stratum, charged with iron and magnesia ; the two re- 

 presenting respectively the overlying granitic and the underlying basaltic layer, the 

 presence of which beneath the earth's surface has generally been inferred from exoplutonic 

 phenomena. The intervention of the argillaceous products of subaërial decay was 

 considered, and the reactions between them and mineral solutions from below, it 

 was conjectured, might give rise to certain micaceous minerals. 



§ ^0. That the great shrinking of the primary layer, consequ.ent upon the removal 

 from it, by solution, of the vast amount of matter which built up the overlying granitic and 

 gneissic series, would result in a collaj)se and a general corrugation of this overlying 

 deposit, and that this would probably be attended by outflows, through fissures, of the 

 underlying basic magma, constituting the first eruptive or exoplutonic rocks, were among 

 the most obvious deductions from this hypothesis. These various points were concisely 

 set forth in notes read in April and May of this year, with the suggestion that this newly 

 proposed explanation of the origin of crystalline rocks, through the action of springs 

 bringing up mineral matters from below, might be called the CRENITIC hypothesis, from 

 the Greek }<pi}y)/, a fountain or spring."" 



§ Tl. The steps in the chronological history of the new hypothesis, which we have 

 sketched in the preceding pages, may be briefly resumed as follows : — 



I. — 1858. An attempt to deduce from the doctrine of a solid incandescent nucleus, and 

 a single primary igneous rock, supposed to be quartzless and basic, through mechanical 

 and chemical agencies, two distinct and unlike classes of sedimentary deposits, which, 

 when subsequently transformed by subterranean heat, should give the two types of acidic 

 and basic crystalline rocks. This was an attempt to adopt the Huttonian metamorphic 

 hypothesis to the conception of a cooling globe, and to give it, what it wanted, a point of 

 departure. 



II. — 1860. An attempt to explain the production, by aqueous action at the earth's sur- 

 face, of various protoxyd-silicates. 



III. — 1863. An attempt to extend this last conception to double aluminous silicates, by a 

 consideration of the formation of zeolites at the earth's surface in rocks of secondary age, 



«' On the Origin of tlie Crystalline Rooks, National Academy of Sciences, Washington, April 15, 1884, in 

 American Naturalist for June; also Royal Society of Canada, Ottawa, May 20, in Amer. Jour. Science, July, 1884, 

 and Nature, July 3, p. 227. 



