Professor Keilhau on Contact Products. 167 



for it shuns no arbitrariness which can advance the cause ; 

 and reasoning in a circle is quite suited to it. In this way it 

 is impossible to approach nearer to indications of the real 

 truth ; on the contrary, by such a mode of proceeding, the path 

 to truth is blocked up. 



The following is the undisguised and true geognostical re- 

 sult as to the subject of which we are now treating : that where 

 two different rocks have been in contact with each other for 

 a long time, there occur, in innumerable cases, peculiar mineral 

 masses, in whose formation this meeting of the two rocks must 

 have performed a very essential part. As, at least in many 

 of these cases, it is quite certain, that the two touching rocks 

 have always had only an ordinary temperature, that hypo- 

 thesis (which is, moreover, of little use in explaining the phe- 

 nomenon) must be rejected, according to which it has been 

 assumed, that the one or the other of the meeting rocks was 

 in a hot condition during the formation of the new masses. 



As, however, from the plan adopted, this datum is falsified, — 

 a datum which at once procures for us insight into the sub- 

 ject, and, at all events, ought to be regarded as extremely 

 important as a point of departure for new investigations, — these 

 fruits cannot be attained, and the opportunity of advancing 

 thus afforded, is lost ; and in this way, not only geology 

 suffers, but even chemistry, for the love of which such 

 sacrifices are believed to be made. The loss thus caused to 

 geology is really incalculable. Since Nature has it in her 

 power, without fire, and, as it appears, without water, to call 

 forth such products as the contact-formations, is it not madness 

 continually to attend only to the fire and water hypotheses, in 

 treating of the origin of the many problematical mountain 

 rocks and mineral masses. I cannot here leave unnoticed two 

 cases in which what we are taught by the contact-formations 

 must, as it appears to me, be of great use. The first relates 

 to the occurrence in granite, gneiss, &c., of certain completely 

 embeddedminerals, which contain some of the very rarest metals 

 and earths, and of which these may be especially named the 

 allanite, gadolinite, orthite, thorite, and euxenite. Mr Scheerer 

 of Christiania, who has gained so much credit by the chemical 

 examination of most of these minerals, properly considers their 



