plicifyof ihc language in which they are expressed) in the Chapter of hh Element* in which 

 he treats of the ptu tonic rock*, and in which he refers them to a deep subterranean source, 

 quotes the following passages from Dr. H^rXxuLtocfi's Syskm of < ■ uolc*jj x-. 



• The ordinary jp-anile of -ifrjrdtfffFijtaVff is the usual ternary compound of quartz, felspar, 

 and mica ; but sometimes hornblende is substituted for the mica. But in many places ;i 

 variety occurci which ii composed simply of felspar and hornblende ; and in examining more 

 minutely I his duplicate com ground , it is observed in some places to assume a line ftrain , 

 □.lid at Jcnjjfli Co bcrnme inidi*tinfpiishablc from the greenstones of the trap family- It attt 

 paused in I ho same uninterrupted manner into a basalt , and at length into a soft claystcue, 

 iriih tftcfrirtose tendency on exposure, in no respect differing from those of the trip i^l in h 

 of the western eoasL 1 ' The same author mention* , atrial in Sftrtiaud , n [jranilc composed of 

 hornblende, mica , felspar, and quart*, graduates in an cojually, perfect, manner into basalt" 

 Mr. Lt&LL □unlitijcs! d In Huntjartf there ore varieties of trachyte r which g geologically * peak- 

 ing , are of modern origin , iu which crystal* not only of mica but of truant* arc earn* 

 mon r together Willi fchpnr uul I torn hi i ti i 1 1- . jj is vm\- [a conceives how such volcanic n\3A- 

 iea may , at aT certain depth from ihe surface t pass downwards kilo granite" (1). 



Tlii-i \< w-t\ Iron, but nlLhdiUrjh the fuels previously cited from Dr, MtcitiuLLeen prove the 

 easy gradation hclwecn basulli® And granitic rocks., they teem as little recondlcablc as the 

 r&eks of Puht Ufovi are wild [J re theory of a Jleecjf-jrily deep (arlarcazi oriyiti of the latter t 

 and less subterranean orinEn of (he former. In Sin^apm-o there are blocks of greenstone as 

 highly crvslal luted as any granite but in which larjje- isolated portbns become com pact and 

 approach to basnH. In these Cases it is impossible to refer the change; from a compact to a 

 crystal line structure merely to the mechanical pressure of the super incum bant crusty for such 

 n force must hare acted uniformity throughout the whole ma$j before solidification. The 

 cause of I he variations in the igneous rocks (excluding those which cool in or near the 

 atmEjfiphnre), murtt be chemical or electrical more than rncchaiiiral. It is probable that Mr, 

 J>AHwm„ iu draw inn attention to the established influence of disturbance in cau&inu certain of 

 the ingredients of a molten mutt of different element s to eryslaUiie and separates from Che 

 m ass j. end thereby attain the |*ower of ascending or descending through it to a different 

 level nccordiiirr to the specific gravity of the crystal, h?H dinearcred a, very potent mecha- 

 nical n^cnt which U subservient to the chemical causes of the gradations in the pi u tonic and 

 Talranic rocta. While bnlinvm|T r however, that Llic influence c<f lomELEioed umFiirri.! prr^urc 

 (and this implies' the absence of disturbance) will he chiefly exhibited in communicating a 

 homo^qTieoois rharacter to (lie iliricl rock * :l i ified under jL , J would not be Tiniiersteed Id 

 limit the effect of disturbance to the mere separation of ingredients by their different rela- 

 tive j|jravi!iefl lL r^Ehcr jippi-jir^ to me that a very imporLatiL np--T:i(iuU of meiihanit-isl agi- 

 tation has been overlooked by Mr, Daiwui. 



This JtNids me tc mii'uv tin; [jest reionrLahlc real Lire of the Pah f'hia rocks t iJicir eubciii- 

 dal f globular j laminar and toned slruture, which I conceive to be intimately connected with 



(I) Lijil'* £kBCRU «r Geology [U *di-j t«1. 1 p. 331 



