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XVIL— ON THE ORIGIN AND PROBABLE STRUCTURE OF 

 THE DOMITE MOUNTAINS OF CENTRAL FRANCE, 

 BY EDWARD HULL, b.a. 



[Read, April 11th, 1881.] 



Last summer, in company with my father Dr. Hull, and Dr. 

 R. Ball, I had the pleasure of examining that remarkable volcanic 

 region which occupies the province of Auvergne, in central France. 

 With Scrope's exhaustive manual in our hands, and aided by his 

 exceedingly accurate maps and faithful descriptions, we had little 

 difficulty in deciphering the physical geography of this some- 

 what complicated region. 



Our explorations, however, were confined to the district of the 

 Puy de Dome, as our time did not permit us to extend our rambles 

 so far south as the Mont Dore district or into Cantal. This 

 region is composed of a central group of volcanic cones and 

 craters, extending long fingers or " cheires," as they are locally 

 named, of lava out into the plain of fresh-water formations, 

 limestones, marls, and alluvial deposits, which form the basin of 

 the Allier river, one of the principle tributaries of the Loire. 

 This region of volcanoes may be divided roughly into two 

 groups : 1, the Domite division, composed of a trachytic form 

 of lava, and pre-eminent alike by their mineralogical character, 

 size, and shape ; and 2, the surrounding volcanic hills, com- 

 posed of scoriae, ashes, and debris, all truncated cones, their sides 

 sloping at the invariable angle of 30° and nearly always with 

 one side broken down and emitting a stream of basalt, which 

 flows for a variable distance over the surrounding country. 



It is extremely probable that, in accordance with a very usual law, 

 these two groups are also divided chronologically ; the Trachytic 

 or Domite hills being of older formation than the basaltic vents, 

 otherwise it is hard to explain the isolation of the former, their 

 bases swept by flows of basaltic lava from the throats of the 

 surrounding craters, and standing completely isolated in shape as 

 in mineralogical character from their nearest neighbours. 



I do not intend to go into the question of the origin of 



