REVIEWS. 86 1 



Geologische und geographische Experiment . Heft III., Rnpturen, 

 Heft IV., Mcthoden und Apparate. By E. Reyer, Leipsic, 

 1894. 



In connection with Professor Walther's book it is interesting to 

 note the appearance of the last pamphlet by Professor E. Reyer, of 

 Vienna, representing the experimental method in geology. The two 

 preceding papers, which appeared two years ago, and which will be 

 more or less familiar to the reader {Ursachen der Deformation und der 

 Gebirgsbildung, Leipsic, 1892; Geologische und geographische Experi- 

 mente iiber Vulkanische-und Massen- Eruptions, Leipsic, 1892), 

 introduced Professor Reyer's experimental work, especially in the 

 reproduction by artificial means of the phenomena accompanying 

 mountain-building and eruption. The last paper, just received, com- 

 prises two sections. The first deals with the various phenomena of 

 cracking and gaping of the crust caused by torsion, lateral pull, lateral 

 pressure, or vertical movement. The phenomena of rupture found in 

 regions of crustal movement or of metamorphism are reproduced here 

 on a small Scale. These experiments recall those of Daubree, but are 

 an improvement over his work in so far as in the present case the 

 materials used correspond more nearly to the materials in nature. In 

 the second part of this paper, where the author gives to the public his 

 methods of experimentation, and the apparatus constructed and 

 employed by him in his laboratory, we find that clay, loess, loam, and 

 gypsum, or some adhesive substance, are the most prominent constitu- 

 ents used, and that ice, glass, or harder substances, do not find a place. 

 The advantage in using softer substances is obvious, for the smaller the 

 scale of the experiment the finer must be the material used and the 

 less, therefore, should be its cohesion in order to make the relation 

 of cohesion to the natural forces, as gravity, correspond to their rela- 

 tions in nature. If the relation be a correct one the action of gravity 

 for instance will produce the same result (of faulting, flexure, etc.) in 

 the reduced laboratory experiment as in the large process in nature. 

 In experiments of torsion with harder substances, as glass or ice, 

 gravity alone produces no effect because the cohesion of the glass is so 

 great. If, however, we have a mixture (of fine-grained silt or gypsum 

 with water) of the proper consistence arranged in thin layers (strata) 

 and leave one part unsupported, the action of gravity alone produces 

 the desired flexure, faulting, or twisting as Professor Reyer has shown. 



