Section III., 1884. [ 1 ] Trans. Roy. Soc. Canada. 



I. — The Orlijin of Crystallme EocJcs. 

 By Thomas Sterry Hunt, M.A., LL.D. (Cautab.), F.R.S. 



(Presented May 20, 1S84.) 



I.— Historical and Cn'iJca/.— Tho .schools of Werner and of Hntton. The chaotic, metamorphic, metasomatic, tlior- 



mochaotic, endophdonic and exopkitonic or volcanic hypotheses. Conditions of the problem. The cre- 



nitic hypothesis stated. 

 II.— r/(e' Dcrdopmcnt of a New Hypothesis.— Tho history of tlie growth of the crenitic hypothesis. 

 lU.—Ilhistrations of the Crenitic Hypothens.— The history oî zoolitic and feldspatliie minerals; of the principal 



protoxyd-silicates, and of other rock-forming silicates. The artificial production of mineral silicates. Tlio 



conditions of the crystallization of minerals. 

 IV.— Conclusions ; followed by an analysis of the contents of sections, and a note. 



I. — Historical and Critical. 



§ 1. The iiroblem of the origin of the crystalline rocks which cover so large a part of 

 the earth's surface is justly regarded as one of fundamental importance to geology, and 

 its solution has been attempted during the past century by many investigators, w^ho have 

 advanced widely different hypotheses. These, it is ]Hoposed to review briefly in a 

 historical sketch before proceeding to suggest a new one, which it is the object of the 

 present memoir to bring forward. Without going back to the speculations of the ancient 

 philosophers, we find those of the last two centuries, Newton, Descartes, Leibnitz and 

 Bullbn, among others, accepting the hypothesis of a former igneous condition of our 

 planet. Starting from this basis, the phenomena of volcanoes, and the resemblances 

 between their consolidated lavas and many of the crystalline rocks, naturally gave rise to 

 the notion of the igneous origin of these, which was formulated in the hypothesis that all 

 su.ch rocks, whether massive or schistose, were directly formed during the cooling and 

 consolidation of a molten globe. 



§ 2. Playfair, in his " Illustrations of the Huttouian Theory of the Earth," tells us that 

 it was Lehman, who, in ll5Q, first distinguished by the name of Primitive the ancient 

 crystalline rocks, described by him as arranged in beds, vertical or highly inclined in 

 attitude, and overlaid by horizontal strata of secondary origin. These primitive rocks 

 were by Lehman regarded " as parts of the original nu.cleus of the globe, which had 

 undergone no alteration, but remained such as they were first created." This view was 

 shared by Pallas and by De Luc, the latter of whom at one time considered the primitive 

 rocks " as neither stratified nor formed by water," though as Playfair informs us. De 

 Luc subsec^uently admitted " their formation from aqueous deposition, as the neptunists 

 do in general." ' 



' John Playfair, loc. cit. pp. 160, 162. The Theory of the Earth, by James Hutton, first appeared in 1785, and in 

 a second edition in 1795. Playfair's celebrated exposition of it, here quoted, was published in Edinburgh in 1802, 



Sec. III., 1884. 1. 



