ANNIVERSARY ADDRESS OF THE PRESIDENT. ci 
of rocks brought into contact with the granite, plastic with water and 
highly heated. 
This communication was followed by one from M. Virlet d’ Aoust, 
on normal metamorphism and the probability of the non-existence of 
true primitive rocks on the surface of the globe. He refers to the 
memoir of Scheerer as supporting the opinions he had previously ad- 
vanced on metamorphic granites, and points out that it is not neces- 
sary, aS is too commonly supposed, that the temperature capable of 
producing normal metamorphism and granitic transformations should 
be very high, since M. Schafhautl has shown that, under pressure, 
steam above 212° Fahr. can dissolve silica, and that probably, as has 
been pointed out by Sir David Brewster, other gases may have con- 
siderably influenced crystallization in altered rocks. M. Virlet con- 
siders that geological discoveries, as well as the advance of inorganic 
chemistry, tend to show that there does not probably exist, and can- 
not now exist, any really primitive rocks on the surface of the earth ; 
that is to say, any rocks which have not suffered some chemical or 
molecular transformation, including water chemically combined, since 
their original cooling. Normal metamorphism, thus extended to all 
the rocks commonly called primitive, is only, he observes, a corollary 
of the theory of central heat and of the original igneous fluidity of 
the earth; conditions during the consolidation of the crust having 
caused changes of surface heat, and the returns of great heat at va- 
rious times having assisted considerably in producing normal meta- 
morphism. M. Virlet refers to the mechanical aggregation of crystal- 
line rocks as affording a proof of general metamorphism, and as due 
to conditions which the researches of Schafhautl, Brewster, Biess 
and Scheerer would lead us to expect. 
In an elaborate account of analyses of some of the siliciferous ther- 
mal waters of Iceland, M. Damour considers that water, acting at a 
temperature of more than 120° Cent., under very considerable pres- 
sure and during a long period, upon the trachytic and zeolitic rocks 
beneath, would dissolve many of the elements of which they are com- 
posed; among others silica, alumina, soda, potash and lime. The 
alumina and lime would not long continue dissolved in the siliceo- 
alkaline solution, while the silica, potash and soda would remain in 
different proportions, as is found in the thermal waters of Iceland. 
M. Descloizeaux communicated the results of investigations made 
jointly with M. Bunsen, of Marbourg, on the two principal Geysers 
of Iceland. Experiments were made in the pipe of the Great Geyser, 
by which it was found that the temperature at the bottom was va- 
riable, being highest immediately before and lowest immediately after 
the great eruptions. It is inferred that the source of heat is not 
situated immediately beneath, but at a distance, probably consider- 
able, and that the column of water communicates by a long and 
winding channel with the space where the direct action of the sub- 
terranean heat is felt. After a great eruption, during which a large 
body of water and steam is ejected, the lower part of the liquid mass 
becomes colder, and the steam arriving from where it is formed, not 
being able to force the water out, is condensed by that filling the 
