222 Professor Hoffmann on the Geological Im^estic/ations 



ingredient which came up with tlie porphyry could unite with 

 the limestone, without its meeting an unsurmountable opposi- 

 tion from the impenetrability of a solid mass. The connec- 

 tion between the augite-porphyry and the dolomite appeared 

 so much the more intimate, from the augite containing a large 

 quantity of magnesia. 



This process, however different it might appear from the 

 previously received ideas as to the formation of rocks, was 

 most ingeniously illustrated by the manner in which the dolo- 

 mite seems united with the limestone. Thus, we do not by 

 any means find, where the limestone, from its proximity to the 

 porphyry, loses its stratification, that it is converted uniformly 

 into dolomite, but we find that the stratification has been 

 broken up and rendered indistinct, partly by confused mixture 

 of the parts, partly by the breaking up of the strata by a mul- 

 titude of fissures running in all possible directions. From 

 these fissures, however, the dolomization proceeds, for their 

 walls consist of crystalline-granular dolomite to a greater or 

 less depth in the neighbouring limestone, and all the small 

 cavities and empty spaces are covered with dolomite druses, 

 and thus the conversion can be effected more or less perfectly. 

 As Buch found throughout the southern Tyrol, that wherever 

 the dolomite occurred, there the black porphyry was at no 

 great distance, he very naturally concluded, that where masses 

 of dolomite present themselves in other portions of the Alps, 

 the black porphyry must be near, and only from some acci- 

 dental circumstance in its position not visible at the surface. 

 His views, therefore, were very perfectly applicable to the 

 whole range of the Alps, and the southern Tyrol might thus 

 be regarded as the key to the complete understanding of the 

 chains of which it is composed. 



The application of this brilliant discovery could, however, 

 be still further extended. Now that attention was so promi- 

 nently attracted to this subject, large masses of dolomite were 

 found in many limestones in other portions of Europe, as in 

 England and the interior of Germany. Wherever porphyries 

 were known to exist (as is so frequently the case in Germany), 

 a more minute examination proved that these must be dis- 

 tinguished into a red and a black, or into quartziferous and 



