Geology and Mineralogy. 133 
——Mr. Delesse has confined his observations, in the work here cited, to the 
with another it traverses, regarding this subject, correctly, as a proper 
introduction to that of metamorphism in general. He divides his work 
into first, the metamorphism of the encasing rock; and second, the met- 
amorphism of the eruptive rock. The different kinds of eruptive and 
encasing rocks are reviewed in order, and afterwards the various exam- 
ples of alteration which have been observed in rear with ea 
either by elesse or other geologists, are carefully dese 
locality and condition of the rocks are described, the pas 2 or pmadlted 
chemical composition. As preparatory to the whole, the 
effects of the “iat action of heat on the various rocks are dwelt upon 
at some len 
relating to cases where the vein is granitic is yet to be published, The 
discussion is preparing the way for the right consideration of the meta- 
morphism of rock strata; and we shall look with interest for the future 
writings of Mr. Delesse on this subject. 
The main difficulty in carrying out the separation between metamorph- 
ism connected with eruptive rocks and metamorphism not so connected, 
arises from the cy seed: of the line pleas off the two groups of altered 
and eruptive rocks from one another. Granitic veins are generally regarded 
as eruptive in all cases ; me yet there i is no evidence : 
grani 
hism—a result of the opening of fissures deep down towards the | 
morp. pening 
interior heat, where heat and water brought in material from 
to fill the eavity, instead of an opening quite througl 
ie Vere ( eneghi 
author of this ca | on the Palzontology of the island of S 
is one of the able corps of io at Pisa, the author of works both 
minerals, fossi 
AR Maths 8 Sardinian formations from the Silurian to the 
