61 
VI. 
SKETCH OF THE OEOLOGY AND MINED AEOGY OF 
THE SHIANT ISLANDS. 
Dy Professor M. Forster Heudle, M.D. 
(President of the Mineralogical Society of Great Pritain). 
Communicated bv J. A. Hauvie-Prown. 
Read •z'jth January, 1880 . 
During tlio Tertiary epoch of the cartli’s formation, and probably 
in Miocene times, its internal fires found out a line of weakness or 
thinness of the crust, perclianco an open rent; or if they did not 
find it out, tliey made it of themselves. Tliis line extended in 
not very devious course, from Antrim, in Ireland, to Yan Mayen. 
This was a good long line, and afforded abundant space for the 
expending of their fury, and the belching forth of their smoke 
and lire, and ashes. ’ 
They e>i;hibitod local partialities, however. Concentrating their 
energies, they overflowed some 1200 square miles in the north of 
Ireland, made a whole island and a volcanic cone, probably of 
14,000 feet in height, at iMull, — a hideous tumbled waste at 
Ardnamurchan,— a grand crater, with an island of dependencies, 
in Skye,— a smaller one in Puim,— little more than a cliff-lined 
chaldron at St. Kilda,— a sprinkling of terraced islands at Faroe,— 
a whole country at Iceland, — and a cone of matchless beauty at the 
northern limits of their dwindling fires. 
There are great gaps in the uniformity of this disposition of the 
centres of energy ; but there may have been many others of which 
no, or almost no relic now remains ; for, after the fire, came the 
water-gravers, in the form of scalping rains, and rutting rivers, and 
gouging glaciers, and battering and undermining waves. Of the 
groat I\Iull volcano only some 3000 feet remain;^ of th.at of Skye, 
little more; of tliat of Ardnamurchan only enough to vouch for 
