﻿ANETVEESAEY ADDEESS OF THE PRESIDENT. xlvti 



silica. Some crystals formed in this way, at the end of a month, 

 attained the size of two millimetres ( = -07874 inch). They were 

 often insulated in an opake paste, sometimes adhering to the sides 

 of the tube, forming true geodes, impossible to distinguish, except in 

 size, from those which crystalline schists often contain. The white 

 substance which forms the greater part of the residue of the trans- 

 formation of the glass is not amorphous, but forms acicular crystals 

 which cannot be better compared than to the dust of fibrous horn- 

 blende passing into asbestus. They proved on analysis to be com- 

 posed of constituents nearly identical with wollastonite. M. Daubree 

 adds, " It is impossible to look without astonishment upon so com- 

 plete a change in the physical and chemical condition of glass obtained 

 by a very small quantity of water, in weight not exceeding one-half 

 of that of the glass so transformed." Under the same conditions, 

 moreover, water exerts an influence on crystallization of the most 

 remarkable kind on quartz and the silicates. At a temperature of 

 about 850° it dissolved the elements that had been combined in the 

 glass by a much more powerful heat, but without its intervention. 

 Its vapour, under the conditions of the experiments, by reason of its 

 acquired temperature and density, acts chemically like water in the 

 fluid state. s 

 In the presidential address of my predecessor, Professor Phillips, 

 in 1859, mention is made of the observations of M. Daubree, of 

 Strasbourg, on the hot springs of Plombieres, then recently made 

 known ; and I now recur to them in greater detail because of their 

 important bearing on the subject to which I am now endeavouring 

 to call your earnest attention, namely, the increasing conviction on 

 the minds of geologists, produced by experiments in the laboratory, 

 that water must have played a most important part in the origin of 

 simple minerals, of the eruptive rocks, and in metamorphic action. 

 M. Daubree made the experiments above described with the water 

 of those springs concentrated to a twentieth of its volume, and he 

 also made a careful examination of their effects upon the mineral 

 substances over which they flow. They rise on the south-west flank 

 of the Vosges Mountains, and issue from a porphyritic granite, — the 

 temperature of the hottest being 78° C. (=172|°P.), and others 

 from 15° to 30° C. (=59° to 86° P.). They contain only a minute 

 quantity of saline matter, not more than half a grain to the quart ; 

 but silicate of potash predominates. The Eomans had formed in 

 it a thick mass of concrete, with channels or gutters, to convey the 

 water to the baths which they constructed in that place, and which 

 still exist. It is composed partly of bricks and partly of the neigh- 

 bouring bunter-sandstein, united by a mortar of lime without sand. 

 This concrete is about 10 feet thick ; and M. Daubree found that the 

 water has filtered through the crevices of the mortar in a continuous 

 stream. The calcareous cement and even the bricks themselves have 

 been partially metamorphosed. The new combinations produced are 

 found especially in the cavities of the mass, where they form mam- 

 millary concretions, sometimes crystallized. The most remarkable" 

 of these in point of number are silicates of the zeolite family, and- 



