150 Geological Society: — . 



to the same kind of concentrically laminated mass, formed by the 

 successive ejection of mass within mass of tough or viscid molten 

 felspathic rock from a central vent below. 



Beyer notices its radiating veins or dykes, their nature and direc- 

 tion as shown by the vesicles in the magma having been dragged 

 out by the stream or current, also its central tuff basin as the 

 relic of the crater, the groin-like ridges radiating from the tuff 

 centre, and the radiating lines of erosion on the surface. 



He also points out that the two most simple of the typical 

 kinds of volcanos are : — 1. The tuff cone ; 2. The effused or efflu- 

 vial volcanic hill (Quellkuppe), more or less dome-like. In the 

 first case a highly hydrous magma, issuing from a fissure, and 

 resolving itself into dust, has assumed the well-known conical 

 form. In the other case a magma with less water in it has welled 

 out, and, according to its consistency, and the levelness or slope of 

 the ground, has either formed itself into a dome-like and bulbous 

 hill, or has spread over the surface as a stream. 



These types, however, are rarely met with in the simple form ; 

 most volcanos have something of each kind. The Kammerbiihl, 

 near Egra, is one of the least complicated instances of the associa- 

 tion of the two types. Dana and Yon Seebach divide volcanos into 

 Ejection-volcanos and Tuff- volcanos, with reason. 



The type represented by the Kammerbiihl may be theoretically 

 varied in several ways : — 1. Had the eruptive fissure on which the 

 Lesser Kammerbiihl stands been larger, repeated eruptions would 

 have taken place, giving rise to a larger isolated volcano, with a 

 central tuff-cone, radiating veins, and peripheral streams. 2. Had 

 the fissure reached the surface at more than one point, a volcanic 

 series would have resulted. 3. Had the points of eruption been 

 very near one another, they would have given rise to a volcanic 

 ridge (a series united by fusion, or an elongated cone). The Bohe- 

 mian forms of volcanos can be readily ranked under the above- 

 mentioned types. As to their local distribution, M. Jokely men- 

 tions one case of serial arrangement along a line striking N.E. 

 Most probably there are more than one linear series of fissures (as 

 in other countries), and these all parallel to the Erzgebirge. 



XX. Proceedings of Learned Societies. 

 GEOLOGICAL SOCIETY. 



[Continued from p. 74] 



January 7, 1880.— Henry Clifton Sorby, Esq., F.R.S., President, 

 in the Chair. 



THE following communications were read : — 

 1. "On the Portland Eocks of England." By the Rev. J. F. 

 Blake, M.A., F.G.S. 



The author gave a general account of the relation of the several 

 Portland rocks in the areas of their development to each other, and 



