1835.] and Porphyritic Greenstone RocJiS. 4S1 



The augite porphyry of Tisenz, in Tyrol, resembles closely 

 that of Nicolajewsk. Those of Steben, in the Fichtelgebirge, 

 and Holmestrand (South Norway), have a deeper basis ; 

 the crystals in the Fichtelgebirge are of a pistachio green 

 colour, and small in number; in Holmestrand they are 

 greenish-black, very abundant, and give to the mass the 

 appearance of basalt. The uralite porphyry is more abun- 

 dant than the augite porphyry. Among the most remark- 

 able varieties are those at Cavellinski and Mostowaja. 

 The basis of the first is greenish-gray, and hard, without 

 labradorite. The crystals of uralite are abundant, and 

 firmly fixed. lorn pyrites occurs in it. The basis of the 

 second is more clear ; the uralite is less firmly fixed. La- 

 bradorite may be observed, but not until the rock is pounded. 

 This porphyry resembles that of Lake Baltyn, which Her- 

 mann has termed Baltynite. The uralite porphyry appears to 

 be more rare in other chains of mountains ; but it occurs in 

 Tyrol; in Mysore (India), at Newstadt; the basis is blackish- 

 green ; the crystals of uralite are small, but distinct. 



Such are the great divisions into which the greenstones 

 may be separated. They are mostly found in primitive or 

 transition slates, and particularly in talc slate, chlorite slate, 

 and clay slate, as in the Uralian mountains, or in clay slate 

 and greywacke, as in the Hartz, and Fichtelgebirge. They 

 resemble some of the primitive rocks. Thus, diorite is an- 

 alogous to syenite ; but syenite is a mixture of grains of fel- 

 spar and amphibole, generally black, or albite is seldom 

 found. It is further distinguished from diorite, by being 

 generally found with granite, or red porphyry. 



Hypersthene rock resembles dolerite, which is a mixture 

 of grains of labradorite and black augite, and accompanies 

 basalt. Augite porphyry approaches basalt. Amphibole is, 

 however, rare in basalt ; olivine never occurs in augite por- 

 phyry ; the basis of basalt is deeper coloured, and contains 

 augite equally black, and, besides, olivine and amphibole ; 

 the colour of the augite basis is often very deep in many 

 augite porphyries, and reciprocally, many true basalts are 

 met with containing olivine and augite of a fine green 

 colour. Recent lavas closely resemble augite porphyry, 

 such as those of Vesuvius, which contain green augite, and 



2g2 



