Prof. Keilbau on the Present State of Geology. 341 



the vessel, by the subtraction of heat, may cause its external 

 surface to contract, and this may mechanically contract it in- 

 ternally, and so heat may be evolved. This explanation is 

 nearly the converse of the previous one of the steam which 

 has been given. There, a chemical expansion first happens, 

 followed by a mechanical expansion, by which heat is involved. 

 Here, in the metal, a chemical contraction first happens, 

 succeeded by a mechanical contraction, by which heat is 

 evolved. 



On the Mode of Formation of Crystalline Limestone, Contact 

 Products, Crystalline Silicide- Slates, and Unstratified Crys- 

 talline Silicide-Bocks ; with Preliminary Observations on the 

 present state of Geology, and on the Methods of Investigation 

 pursued in that science. By B. M. Keilhau, Professor of 

 Geology in the University of Christiania. Communicated 

 by the Author,* 



It would be a happy state of things if, by means of direct 

 observation, we could every where acquire a perfect know- 

 ledge of the structure of that portion of our globe which con^ 

 sists of the known mountain-rocks,^ and if we could obtain £| 

 clear view of the part performed by each mountain -rock, or 

 generally by each mineral mass, as an architectural element, 

 in a construction so complicated. We should thus create an 

 indestructible basis for geology, and could provide for it a 

 foundation of data really belonging to itself, which would con- 

 fer on it an independence that is at present awanting. It is an 

 acknowledged truth, that we cannot be very doubtful as to the 

 origin of a mountain-rock when the relations of its masses are 

 clearly placed before us ; at least, in such a case, altogether er- 

 roneous hypotheses would scarcely be possible. If, for example, 

 we see that an entirely irregular mass lies between sedimen- 

 tary strata, and branches out into these, we cannot, in refer- 



* This literal translation of Professor Keilhau's manuscript has had the advaiv- 

 tage of his revision. — Edu. 



