Lewiiison-Lesshig s Classification of Rocks. 365 
(e) By pressure the magma can penetrate into fissures. If 
it penetrates prior to crystallization, the dike-rocks dififer from 
massive rocks only in structure. If on the contrary the filling 
of the fissures takes place after crystallization of the magma, we 
have veins constituted of a different magma, an extract from 
the primordial magma, rising under the efTect of pressure. 
Then the vein-rocks dififer from the massive as to chemical 
composition, for example greisen and granite (Harker). 
(f) When the crystals form when they are yet soft they 
can be bent, under, pressure, which Weinshenk calls piez- 
crystallization. We would have then, by the action of pressure, 
often even quite slight, original curved crystals without re- 
course to the theory of dynamic action. At the moment of 
their formation a feeble pressure, such, for example, as the 
surrounding mass exerts at the moment of consolidation, is suf- 
ficient to bend a crystal. The author obtained one bent crvstal 
of augite during his experiments on the fusion of pyroxenes 
and hornblendes in a Fourquignon oven. Hence he distrusts 
dvnamo-metamorphic action. 
Magma tic Diffcretitiation. 
Volcanic inclusions have very great significance for differ- 
entiation, a significance which has been rather misunderstood 
until quite lately. The author cites, in favor of the role which 
they play in differentiation, the following argvmients: 
I. A priori ideas. It is difficult to suppose that a great 
mass of a liquid magma can be in contact with the walls of 
the reservoir without partially fusing them. By removing 
blocks, and by fusiop, the passages to the surface are increased 
in size. It is known that Michel Levy, Suess and others allow 
that, in the case of granites, limestones have been fused and as- 
similated; and that Brogger objects, and asks for the proof, 
since the granites, at least of Christiania, contain only one-half 
of one per cent of lime. But, according to Lewinson-Lessing, 
it is the non-differentiated fundamental magma which assimi- 
lates the limestones, and then, only, occurs the division of the 
magma into two, viz: the granite portion poor in lime and the 
magma of the gabbros which are rich in lime. 
IT. The gaseous products of eruptions, especially steam 
and carbonic acid. The latter may come from assimilated lime- 
stones, and the former from shales. 
