1866. | Hints to Home Towrists. 35e 
volcanic cones sending out each its showers of ash or streams of 
black lava. There are few geological sections more interesting 
than some of those in the Linlthgowshire hills, where alternations 
of trap, ash, shale, limestone, and other strata have been laid open. 
Sometimes, for instance, we find a bed of limestone made up of the 
stems of encrinites and brachiopod shells, and covered sharply by a 
layer of ash. The limestone points out a comparatively clear sea- 
bottom, and in the ash-bed we have proof of a shower of volcanic 
dust and stones, which covered the bottom, and destroyed the 
organisms that happened to be living there at the time. In other 
cases, the upper part of an ash-bed becomes calcareous, and a few 
straggling shells make their appearance, until the bed passes up 
into a limestone, showing how, after showers of volcanic detritus, the 
sea-floor became gradually coated, as before, by a layer of living and 
dead organisms. There are likewise occasional thin seams of coal, 
and abundant remains of plants indicative of sub-aerial growth, and 
over the whole comes usually a bed of amorphous or columnar 
basalt. These sections are easily visited, and deserve to be better 
known. 
In Derbyshire the carboniferous limestone has long been known 
to contain certain beds of contemporaneous trap called toadstone. 
In Ireland also there occur, at Limerick and elsewhere, beds of trap 
and ash intercalated among the limestones of the same formation. 
The only Permian traps and ashes yet noticed in the British 
Islands are those recently described from Ayrshire and Nithsdale.* 
Throughout the western region, from Lough Neagh northward 
by Mull and Eigg to Skye and the Sheant Isles, voleanic rocks play 
an important part. Much, if not most of the basalt, dolerite and 
ash of this tract is later than the chalk, and is at once the newest 
and most extensive mass of volcanic material in the British Islands. 
It has the great advantage, moreover, of beng much better exposed 
to view than the igneous rocks of any other series. The waves of 
the Atlantic have carved it into ranges of lofty cliffs which stretch 
on, league after league, headland after headland, and island after 
island, for a distance altogether of not much under 250 miles. It 
forms the well-known scenery of the Giant’s Causeway and the 
Antrim coast-line, Staffa, and the strange terraced pyramidal hills 
of Mull, and the chain of the inner Hebrides. Much remains to 
be known about this great development of volcanic rocks. In some 
places, as in Antrim and the Isle of Mull, fine clay with leaves of 
trees or layers of ignite have been found intercalated between the 
sheets of basalt. It seems likely that similar interstratifications 
must occur elsewhere, and perhaps in such localities, yet to be dis- 
covered, further evidence may transpire as to the history of these 
post-cretaceous volcanoes, and as to their definite geological horizon. 
* «Geol. Mag.’ for June, 1866. 
