582 
ELEMENTS OF GEOLOGY. 
from the granite is of an earthy texture and blue color, and 
often abounds in corals, becomes a white granular marble 
near the granite, sometimes siliceous, the granular structure 
extending occasionally upward of 400 yards from the junc¬ 
tion ; the corals being for the most part obliterated, though 
sometimes preserved, even in the white ^marble. Both the 
altered limestone and hardened slate contain garnets in 
many places, also ores of iron, lead, and copper, with some 
silver. These alterations occur equally whether the granite 
invades the strata in a line parallel to the general strike of 
the fossiliferous beds, or in a line at right angles to their 
strike, both of which modes of junction will be seen by the 
accompanying ground-plan (Fig. 623).* 
The granite of Cornwall sends forth veins into a coarse 
argillaceous-schist, provincially termed killas. This killas is 
converted into hornblende-schist near the contact with the 
veins. These appearances are well seen at the junction of 
the granite and killas, in St. Michael’s Mount, a small island 
nearly 300 feet high, situated in the bay, at a distance of 
about three miles from Penzance. The granite of Dartmoor, 
in Devonshire, says Sir H. De la Beche, has intruded itself 
into the carboniferous slate and slaty sandstone, twisting 
and contorting the strata, and sending veins into them. 
Hence some of the slate rocks have become micaceous; oth¬ 
ers more indurated, and with the characters of mica-slate and 
gneiss; while others again appear converted into a hard 
zoned rock strongly impregnated with feldspar.”f 
We learn from the investigation of M. Dufrenoy that in 
the eastern Pyrenees there are mountain masses of granite 
posterior in date to the formations called lias and chalk of 
that district, and that these fossiliferous rocks are greatly 
altered in texture, and often charged with iron-ore, in the 
neighborhood of the granite. Thus in the environs of St. 
Martin, near St. Paul de Fenouillet, the chalky limestone be¬ 
comes more crystalline and saccharoid as it approaches the 
granite, and loses all trace of the fossils which it previously 
contained in abundance. At some points, also, it becomes 
dolomitic, and filled with small veins of carbonate of iron, 
and spots of red iron-ore. At Rancie the lias nearest the 
granite is not only filled with iron-ore, but charged with py¬ 
rites, tremolite, garnet, and a new mineral somewhat allied 
to feldspar, called, from the place in the Pyrenees where it 
occurs, couzeranite.” 
Hornblende-schist,” says Dr. MacCulloch, “ may at first 
have been mere clay; for clay or shale is found altered by 
* Keilhau, Gaea Norvegica, pp, 61-63. f Geol, Manual, p. 479. 
