Origin of certain Granites, ^c. 51 



South America, Polynesia, part of Africa, etc., with all requisite 

 appliances at his command, and without having neglected the study 

 of chemistry or mineralogy ; but, even now, must confess that, like 

 most of the continental men of science who have made this subject a 

 special study, he has not yet been able to arrive at any such immediate 

 or sweeping conclusions as Mr. James Grcikie, after his short examin- 

 ation of the Scottish rocks, has been so fortunate as to convince 

 himself of. 



"Without, however, being either a Neptunist, Plutonist, or Hydro- 

 thermalist, he believes that natiu'e has employed all these and other 

 agencies in her metamorphic operations, and is fully prepared to^ 

 become a convert to Mr. James Geikie's or any other's views as soon 

 as a searching but impartial examination of the evidence brought 

 forward convinces him of their soundness. 



In this communication it is not intended to comment upon or 

 question the accuracy of the local geology referred to in these me- 

 moirs ; but it is proposed, as the real object of these remarks, to 

 examine into certain statements and arguments (quite independent 

 of purely local data) made use of by the author in the working out 

 of these memoirs, in order to convince himself of whether they are 

 sound or not, and thereby to arrive at a proper estimate of how far 

 conclusions dependant upon such data are entitled to confidence. 



The perusal of these two papers would, he supposes, produce very 

 different impressions upon different readers : On the mere field ob- 

 server, after skipping sundry little passages, the science of wlilch he 

 could not quite understand, the memoirs in question would read 

 ■ well, smoothly, and plausibly, and in conclusion, probably convinced 

 by the boldness of the style and the apparently indisputable chemical 

 knowledge of one who writes with such ease of chemical re-agents, 

 magnesian, alkaline, and basic properties of rocks,, and explains the 

 actions of the alkalies, magnesia, etc., would, without further inquiry 

 into a subject which always had been a puzzle and a bore to him, 

 be quite content to accept all these new conclusions, and for the 

 future to believe that any stratified sedimentary bed, like grauwacke, 

 etc., can, by the wondrous agency of hydrothermal action, be con- 

 verted in situ into granite, minette, diorite, serpentine, porphyrite, 

 etc., etc., or any other rock. 



On the geologist, however, who possessed even a very small know- 

 ledge of chemistry or mineralogy, a very difi"erent impression would 

 be produced ; he would at once perceive that the chemistry was in- 

 correct in points where even the merest tyro ought not to blunder, 

 and that, to say the least, the petrology was exceeding "loose;" and, 

 unJess he determined to visit the localities and to study the matter 

 for himself, would lay aside the memoirs with the intention of not 

 putting any confidence in conclusions arrived at by the help of such 

 unsound data. 



These remarks may appear severe, and although, as will be seen, 

 they admit of easy and indisputable proof, they have only been here 

 brought forward after serious consideration, and in the firm belief 

 that it is the duty of every geologist not to accept any new -views 



