54 GEOLOGICAL MEMOIRS. 



mospliere ; the whole of the crevices wdthin the hill being occupied 

 by fresh \Yater that resists the upward dhection of the currents. If 

 the whole were covered with sea-water, its depth being but slight at 

 the top of the hill, and supposing that the pressure of fresh water 

 mthin the hill had force enough to keep out the sea-water from all 

 the cracks and clefts of the rock, then, as the height of a column of 

 fresh water within the hill, and that of the sea-water at its base, would 

 be equal in bulk, the difference of the specific gravity of the two 

 fluids would cause the fresh water to ascend in the hill and to burst 

 forth at the top in springs. 



We will now speak of the chemical relations. It is very e^ddent 

 that the iron contained in the Faxoe dolomite has been derived from 

 the water of the springs, because all the suiters of that date, like 

 those which are found in the separated concentric layers, the thickest 

 of them bemg in a semi-stalactitic state, are ferruginous. That, on 

 the other hand, the magnesia of the Faxoe dolomite was not brought 

 hither by the springs, is apparently proved by the fact that the sinter- 

 like masses deposited in the interior of the Faxoe hmestone do not 

 contain an essential quantity of magnesia. 



The composition of the Faxoe dolomite is — 



I. II. 



Carbonate of lime 80-67 79*89 



Carbonate of magnesia 16*48 17=03 



Silica 0-81 0-65 



Iron (Argilla?) 2-04 1*29 



Water and loss 1*14 



100-00 100-00 



In the first analysis the lime was not weighed, and the water and 

 loss were not calculated. 



The yellow sand-like limestone which contains the dolomite is 

 composed of — 



Carbonate of lime and loss 95-75 



Carbonate of magnesia 0'64 



Ferruginous silica 2*74 



Iron 0-87 



100-00 



I have at the same time made analyses of the Faxoe hmestone and 

 of the upper limestone, both of which contain a very small proportion 

 of magnesia. 



Yie learn then from chemical analysis that all the limestone at 

 Faxoe has been deposited by sea-water by the intervention of animals, 

 and that the dolomite contained in it, and either contemporary with 

 it or of an anterior or posterior date, contains just such a proportion of 

 magnesia as corresponds to that which the marine, lime-secreting 

 animals always contain. The sinter deposited in the crevices of the 

 coral-rock, and derived from the fresh spring- water, contains also only 



