1 22 TJie American Geologist. August, i89s 
nient of balls and sponges of silica, the microscopic cr>'stals of 
orthoclase and of albite in the stratified rocks. (Lory, Cay- 
eux); they give rise to various forms of silica at the outcrops 
of the Gypse (Munier-Chalmas), they calcify or decalcify 
(Termier) the basic rocks and they dealkalinize the acid; they 
produce important rearrangements (de Launay) in metallifer- 
ous de])osits. xA.t a distance from granite contacts black mica 
is much developed, also various silicates of alumina, and nearer 
the contact alkaline feldspars are formed. Lacroix hds shown 
that in the massive Iherzolytes of the Pyrenees, which are en- 
tirely destitute of alkalies, the micas are developed, also alka- 
line feldspars and tourmaline, all minerals of the alkaline mag- 
ma. Here the action of transfer by fumaroles is undeniable. 
De Lapparent has dwelt on the importance of solfatrine ac- 
tion accompanying modern acid eruptives; and it is known 
that certain dykes of granulyte and of pegmatyte act like con- 
cretionary veins. This fact was early known and is con- 
firmed by numerous observers. The Stockwerks of Zinnwald 
and of Altenberg furnished many examples of this to our pre- 
decessors. 
The author, finally, presents a brief expose of the hypothe- 
sis which he proposes for the forms and variations of igneous 
rocks. The active agent of these alterations is believed by 
him to be the circulation of liuids under pressure and at a 
high temperature through the reservoirs containing the erup- 
tive magma. These reservoirs are filled (i) with the ferro- 
magnesian magma which serves everywhere as a scoria for the 
impure covering or iron button of the internal mass of the 
globe, the interior mass being considered essentially irony; (2) 
the rock-products of this button, such as the alkalies, 
alumina, silica, which are removable by mineral agents: (3) 
the result of a refusion of the lower parts of the crust by the 
rising of the isogeotherms, whether such rising be due to an 
increase of thinness of the crust or to an ascent of large 
.masses of the fused magma. These circulating- fluids com- 
bine, under conditions favorable for the operation of the law of 
Soret, to produce dififerentiations, the alkaline substances al- 
ways rising and the ferro-magnesians tending to descend. 
Hence the first to appear, in case of volcanic action, is the al - 
