Cri/8lalline Silicide Bocks. 173 



authorities in the science. It will doubtless be thought improper 

 that I should venture on such an assertion, but I cannot keep 

 it back, as I am firmly convinced that it is true, and that it is 

 necessary to make it. It is undeniable that the difficulty is 

 very great of attaining to a perfect knowledge of the relations 

 of the rocks under consideration. It is only at very few points 

 — and even these are for the most part very difficult of access, 

 and are frequently remote — ^that these rocks are displayed in 

 such a manner as not to be misunderstood. Most observers only 

 see localities which are of such a nature, that, in their case, theo- 

 ries and imagination come to form the chief part of that deline- 

 ation of the natural phenomena it is the object to produce.* 

 When this takes place with those who make a personal exa- 

 mination of the subject, we may easily form an idea of the 

 situation of the geologists who must derive their information 

 from descriptions.t The deficiency of knowledge can thus 

 be excused ; but still it exists. Were this not the case, — did 

 the many geologists who believe that it is not their province, 

 but that of the chemists, to decide on the question as to the 



was excavated among the ruins of the Chapter-house of the Cathedral of St An- 

 drews. 



* The following is a most remarkable example of the extent to which this may 

 proceed with even the most experienced observers. In several parts of Sweden, 

 as is well known, horizontal transition strata are found reposing on an ancient 

 surface of rock, which consists of the upright ends of beds of gneiss. Nothing can 

 be more certain and more simple than this ; and the relation can be directly and 

 distinctly observed at many of the points where the two systems of strata meet 

 each other. Nevertheless, it lately escaped the observation of one of the most 

 practiced geologists. During his last visit to Sweden, Von Buch was so far from 

 being able to notice it, that, on the contrary, he asserts that *' the gneiss is never 

 in contact with these transition strata, but remains everywhere at a distance, and 

 with a distinct margin." — (Neues Jahrbuchfiir Mineralogie, 1842, p. 282.) From 

 this result of his examination of the localities, the author then forms some most 

 singular ideas regarding the internal structure and origin of these mountains. 



t The geological authors and teachers belonging to the last class, who nnfor* 

 tunately are not few in number, are, however, just the individuals who feel 

 perfectly assured on the subject. As an illustration, I may instance a Gei-man 

 schoolman, who perhaps never saw a mountain, but has felt himself called upon 

 to write a book on " The Constitution of the Globe" He says, that, with the che- 

 mical reasons for the formation of granite from the melted state, those also agree, 

 which are derived from positional arrangement ; and these, he asserts, are quite 

 decisive ; while, according to his opinion, some objections might be made to the 



