48 
THE PRINCIPAL FLOOR. 
name of Drift. A system of colouring exhibits the distribution 
of the several formations, including these superficial deposits ; 
but by exposure to the light, some of the colours have faded. 
A map on the same scale is, however, mounted on rollers under 
the neighbouring gallery, and the colours are here well pre- 
served. For further information the visitor should consult the 
Guide to the Geology of London (price, Is.), written by Mr. 
Whitaker in explanation of this Model and of the Geological 
Survey Map of London and its Environs. 
Model of the Chain of Puys, Auvergne. — Presented by the 
late G. Poulett Scrope, M.P . , F.R.8., dee. No. 43. 
Little more than a century ago two French travellers returning 
from Italy observed that the rocks in certain parts of their 
route through Central France bore a striking resemblance to the 
volcanic products of Vesuvius. Although at first received with 
considerable opposition, the truth at length became established, 
that at a comparatively recent geological period the interior of 
France had been the theatre of energetic and frequently-repeated 
volcanic action. One of the most interesting groups of these 
extinct volcanoes is represented in the model before us, which is 
placed opposite to the model of London, one being on each side 
of the Central Vase. 
The volcanic hills of the department of the Puy-de-Dome form 
an irregular chain, running nearly north and south, and rising 
from the granite plateau which forms so prominent a feature in 
the geology of Auvergne. The surface of this granite presents 
several depressions, formerly occupied by lakes, the existence of 
which is now marked by certain fresh-water deposits, of which the 
largest forms the fertile plain of the Limagne, represented on 
the eastern side of the model. Passing westward from the 
valley of the Allier, we cross the calcareous marls and other 
lacustrine deposits on the margin of the Limagne, and reach the 
eastern escarpment of the granitic table-land which, extending 
in width for about 12 miles, slopes on the western side to the 
valley of the Sioule. The chain of “ puys,” which rises from this 
platform, includes about 70 volcanic hills, of which the largest is 
the Puy-de-Dome, a mountain rising 4,844 feet above the sea- 
level. Most of these hills are composed essentially of the scoriae, 
lava, and other volcanic products, which, accumulating around 
the orifices of eruption, have formed conical hills, often presenting 
at the summits well-defined craters, from which, in many cases, 
distinct streams of lava may be traced. The Puy-de-Dome and 
a few other hills consist of a peculiar trachytic rock called, from 
this locality, domite. 
In the drawers beneath the model is an interesting group of 
rock specimens illustrating the peology of the district, presented 
mostly by Prof. C. Le Neve Foster, F.R.S. 
