20 THE CANADIAN NATURALIST. [Feb. 



have seen, to take its part in the crystallization, in some cases 

 forming hydrated minerals; and the excess of it, as Mr. Sorby sug- 

 gests, passed up as a highly heated liquid, holding dissolved 

 materials, which would afterwards be deposited in the form of 

 mineral veins in the fissures of superincumbent rocks. 



I have thought it well to give at some length the remarkable 

 results and conclusions by Mr. Sorby, because I conceive that they 

 have not as yet received the full degree of consideration to which 

 they are entitled, and are perhaps little known to some of my 

 readers.* The temperature deduced by him from the examination 

 of the crystals of hornblende and feldspar from Vesuvius is 

 curiously supported by the experiments of Daubree; who obtained 

 crystallized pyroxene, feldspar, and quartz, in presence of alkaline 

 solutions, at a temperature of low redness ; while De Senarmont 

 crystallized quartz, fluor-spar, and sulphate of barytes in presence 

 of water, at temperatures between 200^ and 300° C At the same 

 time the deposits from the thermal waters at Plombieres show 

 that crystalline hydrous silicates, such as apophyllite, harmotome, 

 and chabazite, have formed at temperatures but little above 80° C, 



We conceive that the deeply buried sedimentary strata, under 

 the combined action of heat and water, have, according to their 

 composition, been rendered more or less plastic, and in many cases 

 have lost to a greater or less degree the marks of their sedimen- 

 tary origin, although still retaining their original stratigraphical 

 position. In other cases they have been displaced, and by pres- 

 sure forced among disrupted strata, thus assuming the form of 

 eruptive rocks ; which, becoming consolidated under a sufficient 

 pressure, retain the same mineral characters as in the parent beds. 

 It is only those rocks which, like lavas, have solidified at or near 

 the surface of the earth, and consequently under feeble pressure,. 

 which present mineralogical characters dissimilar to those of the 

 undisturbed crystalline sediments. With this exception, the 

 only distinction which can be drawn between stratified and 

 unstratified masses must in most cases be based upon their attitude^. 

 and their relation to the adjacent rocks. 



In view of these considerations I have, in previous papers, adopt- 

 ed for geological purposes a division of crystalline rocks into 



*See further the late observations of Zirkel confirming those of Sorby. 

 Proc. Imp. Acad. Vienna, March 12, 1863 ; in abstract in Quar. Jour.. 

 Geol. Soc, vol. xix. 



