160 Professor Keilhau on Contact Products. 



of all those masses regarded as eruptive, it refers to the great 

 central reservoir, it is undoubtedly extremely attractive on ac- 

 count of its simplicity and intelligibility. When, however, it 

 is required, that not only the rocks composed of silicates, but 

 also limestones, therefore, in short, the most heterogeneous 

 masses, are to be regarded as having burst forth from the in- 

 terior of the earth, this theory, as has been remarked by others, 

 no longer possesses the qualities just mentioned ; for, instead 

 of producing light, it only leads us into still greater darkness. 

 If, however, it should be the case that the geognostical phe- 

 nomenon in question is less correctly represented for the pur- 

 pose of rendering the eruption-hypothesis available, it must be 

 confessed that that doubtful relief is dearly purchased. I do 

 not, indeed, venture to assert that the description quoted of 

 the phenomenon at Auerbach is incorrect, for it scarcely con- 

 tains any absolute impossibility. It can very well be supposed 

 that the gneiss received from above the upfilling of limestone 

 into an existing fissure, nay, if necessary, we may even ima- 

 gine a filling proceeding from beneath, and standing in no 

 connection whatever with volcanic action; for, it might be 

 assumed, perhaps, that an internal mass of limestone had been 

 brought to the state of a sort of moya, in some way or other, 

 for example, by the movement of the overlying rock and the 

 entrance of water, and that in this way it could be pressed 

 upwards into the fissure. But the real question is, if we have 

 here actually before us a filling up of a fissure, and if the phe- 

 nomenon has not assumed that character in the description on 

 account of the theory. Leonhard terms the mass a vein, and, 

 from his sketch, the conclusion must be drawn that it really 

 cuts through the gneiss strata ; but, in the description which 

 I have seen {Leonhard^ s Populdre Vorlesungen iiber Geologie, 

 vol. ii. p. 215), this latter and most important circumstance is 

 passed over in silence, which seems not a little suspicious. Is 

 it not the case here, as has undoubtedly happened in other si- 

 milar instances, that an error has been committed in making 

 a vein of a mass which ought, perhaps, more correctly to be 

 included among the beds \ 



But it is now time to close these remarks on contact-pheno- 

 mena, and to pass to another important subject, in the consi- 



