Notice of Active and Extinct Volcano*. 946 



not in our power to do. Suffice it to say, that the trass or tar- 

 ras, of the Rhine, so esteemed as a subaqueous cement, is a 

 volcanic production, and that the evidence is generally of the 

 same nature as that which relates to the volcanic district of 

 France. The trass is regarded by all as pumiceous conglom- 

 erate ; it exists in vast quantities, but geologists are not ex- 

 actly agreed as to the mode of its deposition — whether it is 

 an ejection from craters, in the form of ashes, or a muddy 

 eruption like those of South America. 



Hungary. 



Professor Daubeny visited Hungary as well as the volcanic 

 regions on the Rhine, and he has availed himself of the 

 elaborate work of Beudant, which describes in full detail this 

 interesting country. In the opinion of our author, Hungary 

 is the country which should be principally examined in study- 

 ing the natural history of trachyte, which plays so important 

 a part in the ancient volcanos — as trachyte appears to be 

 little known in this country, we will quote the account of this 

 substance which Prof. Daubeny has abstracted from Beudant, 

 and we do it with the more satisfaction as we are in possess- 

 ion of Beudant's work, and an extensive suite of trachytic 

 rocks, from Hungary, which were put up at Vienna, and la- 

 belled with great care, and with a very judicious selection of 

 excellent characteristic pieces.* We have compared them 

 with the following description, and have great reason to be 

 satisfied with its accuracy. 



Trachyte includes five varieties : — 



1. Trachyte properly, so called. 



2. Trachytic porphyry. 



3. Pearl stone. 



4. Millstone porphyry. 



5. Trachytic conglomerate. 



" Trachyte, properly so called, is characterized by its porphy- 

 ritic structure, by the scorified and cellular aspect which it has 

 such a tendency to assume, by its harsh feel, and by the presence 

 of crystals of glassy felspar, generally cracked, and sometimes 

 passing into pumice. Besides these, which may be regarded as 

 essential to its composition, crystals of mica and hornblende are 



* They have been added by, Col. Gibbs, to the great collection purchased oi 

 him for Yale College, in 1825. 



