STUDIES IX EXPERIMENTAL GEOLOGY. 201 



paper around the glass so as to make the fragments keep their places 

 and preserve their relative distribution to each other, he found that 

 the fractures, instead of assuming a uniform direction, formed in the 

 glass a network of geometrical regularity. They seemed to be grouped 

 in two directions or systems, equally inclined to the axis of torsion. 

 The two conjugate systems of fractures generally crossed each other 

 at very open angles, the measure of which depended on the relative 

 dimensions of the two sides of the plate. Sometimes the angle was a 

 right angle, sometimes it was reduced to an angle of 70 or less. 



These artificial fractures present close analogies with certain geo- 

 logical characteristics of different regions. An example of localities 

 in which a correlation is presented between the subterranean fractures 

 and the reliefs of the surface is presented in the cretaceous beds of the 

 south of France. If we examine attentively a well-made map of this 

 district, we shall see that from the principal valleys, which are parallel 

 to each other, branch out a large number of other valleys, likewise 

 rectilinear and parallel with each other. "We can see in them how the 

 thin pellicle which we call the crust of the earth has yielded to strains 

 or torsions analogous to those which the wrench has impressed upon 

 the plate of glass, and how it has become fissured in directions co- 

 ordinate to each other. In the Spanish part of the massive Mont 

 Perdu, the cretaceous and nummiliferous rocks, in the main horizontal, 

 have been raised to a height of nearly ten thousand feet, and are 

 notched to the depth of four or five thousand feet by narrow valleys, 

 the walls of which are nearly vertical. Another example of this kind 

 of reticulated system is presented in the forms of the coasts, fiords, 

 and principal valleys of a part of Norway. 



We already know that the schistous or leafy structure presented by 

 many tracts called metamoi^hic must be attributed to real laminations. 

 M. Daubree has make experimental studies on the distortions which the 

 forms of the fossils in the schistous rocks have undergone. The trilo- 

 bites and mollusks of the neighborhood of Angers very rarely present 

 themselves in any other than deformed shapes which seem like carica- 

 tures of the animals from which they are derived. These deformities 

 can be perfectly imitated in experiments. If we inclose the shell of a 

 crawfish in a mass of lead which we then cause to pass through a flat- 

 tening-mill, we can inflict upon the crustacean a malformation quite 

 like that of the silurian trilobites. A remarkable exemplification of 

 the changes of form which fossils contained in rocks that have become 

 schistous have undergone is presented by the belemnites of different 

 localities in the Alps, in cases where they have been broken into pieces 

 and their segments have been more or less removed from each other. 

 M. Daubree has produced similar forms of breakage by laminating 

 blocks of lead in the interior of which belemnites had been previously 

 inclosed. Fig. 2 represents a belemnite thus inclosed in a block of 

 lead of which only a half is shown. The effect of laminating is shown 



