182 Mr. A. Gages o?» Pseudomorphic Tremolite. 



The mineral analysed may therefore be considered as a mixture 

 of dolomite and calcite in the following proportions : — 



CaOC02 + MgOC02 .... 90-26.2 

 CaO C02 9738 



100-000 

 The insoluble skeleton^ when dried, had the appearance of an 

 asbestiform tremolite, and its analysis gave the following re- 

 sults : — 



Silica 68-181 



Magnesia 28-909 



Alumina with traces of iron . . 2-181 



99-271 

 It is probable therefore that the skeleton was tremolite, from 

 which watei-j impregnated with carbonic acid, had removed the 

 whole of the lime. Thus if we deduct the per-ccntage of lime 

 and calculate the remaining numbers in 100 parts, in the ana- 

 lysis of a specimen of tremolite from Wermland made by Bons- 

 dorff, and compare the results with the preceding analysis of the 

 skeleton, wx shall get the following numbers : — 



Tremolite from Tremolite, supposing 



Wermland aua- 

 Ij'sed by BonsdorfF. 

 Silica . . . . 59-75 



Lime 1411 



Magnesia . . . 25-00 

 Protoxide of iron . 0-50 

 Pluorine . . . 0-94 

 Water . . . . 010 



100-40 100-464 



The water which exists in the mineral evidently belongs to the 

 skeleton ; but as its quantity could not be absolutely determined, 

 owing to the presence of organic matter, I have not attempted to 

 calculate a formula for the asbestiform skeleton. 



Another explanation of the origin of the skeleton suggests 

 itself, namely that the mineral was not hornblendic, but augitic j 

 for example, like the asbestiform diopside from Zillerthal, ex- 

 amined by Meitzendorff. When augitic minerals are acted upon 

 by water containing carbonic acid in solution, the lime is removed 

 and nearly the whole of the magnesia is left behind, of which the 

 Rensselserite of Beck is an example. Numerous other examples 

 of this kind have been given by Beudant, Svanberg, &c. 



Whatever may have been the original mineral, it must have 

 been considerably modified before the encrustations began. The 

 proportions which the skeleton bears to the whole mass of the 



