I 



Notes on Professor 'KeUhaii^s Paper on Granite, S^c. ^^ 



ranged according to that division of the two modes of formation of crys- 

 tals, &c.) " We ought first of all to inquire, if the fact that substances 

 in the state of an elastic fluid can be solidified in crystals, could be capa- 

 ble of application here; but even the first glance shews us," &c. P. 96, 

 last line. " The dolomite theory supposes that the dolomite has been pro- 

 duced by the penetration of magnesia exhalations into masses of carbo- 

 nate of lime. We ought, according to what we have said, to regard 

 this hypothesis as a very legitimate one, although it goes far beyond 

 what is taught us at present by chemistry. But what arrests us in this 

 theory is, that, in order to support itself, it requires the assistance of 

 other hypotheses of a very arbitrary description. It cannot be denied 

 that in some places dolomite occurs in very thin but extensive strata, 

 and quite in a regular manner between other beds ; now, we cannot 

 see why the magnesia should go and lodge itself precisely in those beds 

 -which are to be transformed, while it passes by, without producing 

 change, those which preceded them in the order of the strata." (The 

 dolomite is often found contained in carbonate of lime, and there are 

 therefore unaltered beds beneath those which are converted into dolomite.) 

 P. 96, 1. 31 ; " Thus, if we suppose that these substances introduced 

 into the rocks came from below, we might say that the great porphyry 

 formation in our transition district is to be ascribed to the circumstance 

 of the emanations having been lodged in the sandstone part of the series, 

 while, on the other hand, the substances necessary' for the formation of 

 the eurite-porphj'ry had not been elevated to that height, but had united 

 themselves to certain strata in the vicinity of the primary rocks, and so 

 forth. But, in considering the subject more closely, we ma}' leave out 

 of consideration all these artificial speculations, and do not require to 

 think of emanations, whether with reference to dolomite or to crystalline 

 iTOcks. Wc are undoubtedlj' placed in obscurity here, and an obscurity 

 ^lich the lights of chemistry will probably not clear up for a long time; 

 it is therefore of little use to trouble ourselves with hypotheses, in which, 

 no doubt, homage is rendered to chemistry, but wldch can only be half 

 acknowledged by chemistry." — P. 97, 1. 15 ; " We are undoubtedly in 

 possession of (he following two most important facts : First, that masses 

 in a solid state can crystallize, or undergo morphological changes, with- 

 out its being necessary, so far as we can sec, tliat they should previously 

 pass into one of the ntutes of fuiditij with which we are acquainted; and 

 next, that substantially newly-formed bodies, crystallized or uncrystal- 

 lized, can be developed in compact masses likewise, without our remark- 

 ing that the matter, immediately before the formation of the new body, 



has been in one of the states of fluidity known to us For my 



own part, ever since I directed my attention to these, though obscure, 

 yet important facts, I have always attributed an increasing value to them. 

 Even in ltt28, 1 endeavoured to bring prominently forward, and to prove 

 this position, \'v/.. that one (f the hitherto known forms of aggregation in wliich 

 ■tuhatane.es exist in a fluid state, does not uecessarilij precede the formation or 

 tmnt formation of solid bodies ; hut that, on the contrary, the rompact farm 



