358 Prof. Keilhau on the Formation of 



product in question, under precisely the same circumstances 

 as those under which the said product must have had its ori- 

 gin ; in short, if there be theorists who endeavour to tread on 

 safe ground, and who wish only to ascend from what is known 

 to what is unknown, then assuredly we are those theorists ! 

 And it is so much the more easy to be thus misled, because 

 the doctrine of these theorists is so simple, and can be under- 

 stood with so much facility. All difficult details of the sub- 

 ject are necessarily kept at a distance, for if they were intro- 

 duced, the whole theory would be destroyed. 



At present, all that can be legitimately asserted (by mak- 

 ing full use of " what is known"* connected with the ques- 

 tion) regarding the marble which occurs so frequently at the 

 contact of another rock, but which, in other respects, belongs 

 to some uncrystalline deposit of limestone, is limited to the 

 following : a. That it must be considered as a product of that 

 probably very slow process by which crystallizations and che- 

 mical results generally, are effected by modes of operation 

 which either cannot be at all imitated by art, or can be so 

 in but a very imperfect manner ; and, b. That the actions 

 which took place were either caused, or, at least, greatly 

 assisted by the contact of the limestone with the other rock 

 of an entirely different description. 



We may conjecture that it was electricity which here per- 

 formed a principal part ; we may willingly consider the phe- 

 nomenon as the result of a " molecular action" that has taken 

 place in the solid mass ; we may speak of " concretionary ac- 

 tions" (Murchison, i. 360), of " corpuscular forces," &c. ; in 

 short, we may proceed as if we knew something of the pro- 

 cesses which were in operation : but it must still be allowed 



* Hitherto no one has brought all this together. Among the circumstances 

 which belong to those that bear on this matter, we may also include what is 

 known respecting the distance from the line of contact at which the limestone 

 begins to be granular, and also the power of conducting heat possessed by melted 

 rocks. As to the first point, I can instance that the dark compact limestone of the 

 Christiania district begins to become light-coloured and crystalline at a distance of 

 4000 or 5000 feet from the granite ; and, regarding the second, that, on Mount 

 Etna, an old stream of lava has been seen reposing on a mass of ice, over which 

 it had been poured, just as in Iceland lava-streams have been found resting on 

 ttill existing glaciers. 



