LEONHARD ON PORPHYRY. 7 



the earth's surface, commencing with Saxony, Bohemia, and other 

 parts of Germany, and extending to America, Egjrpt, and AustraUa 

 (p. 64-1 10). To this section the author adds a list of the geological 

 maps on which the occurrence of porphyry is noted. 



The second portion of the work relates to the connection between 

 porphyry and the stratified and unstratified formations. After al- 

 luding to the history of the subject and the opinions held by the 

 earlier cultivators of the science, the author states (p. Ill) that 

 Hutton was the first who attempted to establish any real notion re- 

 specting the probable origin of this rock. The occurrence of granite 

 in the micaceous slate of Glen Tilt led him to the idea that the for- 

 mer had penetrated the latter, and was consequently younger. He 

 extended this theory to porphyry, and in vain attempted to introduce 

 it among the followers of Werner. It was only after the commence- 

 ment of the nineteenth century, that the idea, that porphyry and 

 other rocks, hitherto reckoned amongst the primitive formations, 

 had been produced by the operation of fire, acquired any credit. The 

 journeys of L. v. Buch in Norway and Lapland, and of Hausmann 

 in Scandinavia, had great influence in producing this result. Por- 

 phyry-dykes are first mentioned in the works of these two travellers 

 as penetrating clay-slate and transition limestone. Equally important 

 were the observations made by the Swedish author Strom, in 1812, 

 in the neighbourhood of Freiberg. He must be considered as one of 

 the first who opposed the then prevailing idea of the stratified na- 

 ture of porphyritic masses. MacCulloch, A. Boue, and others wrote 

 decidedly in favour of the eruptive nature of porphyry ; and finally, 

 as the author states (p. 1 13), we have a work, respecting the forma- 

 tion of porphyry, by the Mining Councillor Schmidt, who is so well 

 acquainted with the geological relations of the Rhine district, in which 

 he points out the many analogies between this rock and basalt, and 

 states his conviction that porphjrry has risen through the crust of 

 the earth in an igneous, fluid state*. 



During the last twenty years these views have become almost 

 universal. In various and distant countries observations have been 

 carefully recorded respecting the occurrence of quartziferous porphy- 

 ries with stratified and unstratified rocks, the most important phse- 

 nomena of which are subsequently described. 



We can only briefly notice the difl'erent heads into which the au- 

 thor has subdivided the subject (p. 106-186). 



I. Porphyry and the abnormal formations. The relations of 

 porphyry with gneiss, mica-slate, granite, syenite, hornblende-slate, 

 diorite, serpentine, crystalline limestone, and melaphyre ; describing 

 all the principal localities where it occurs under the difl'erent circum- 

 stances. 



II. Porphyry and the normal formations. 1. The relations of 

 porphyry with the Greywacke formations ; 2. the Carboniferous 

 system; 3. the Rothliegende or Permian; 4. the New Red Sand- 

 stone ; 5. the Jurassic system ; 6. the Cretaceous formations : and 

 the relations between crystalline limestone and porphyry. 



III. Plutonic and volcanic formations newer than porphyry. 



* Karsten's Archiv fur Bergbau, vol. vii. p, 195 et seg., 1823. 



