GllINDLEY — GEOLOGY OF THE ISLE OF MAN. 
179 
great, as it includes the whole of the Manx Carboniferous series, the 
Devonian conglomerate, and a considerable portion of the underlying 
schists. Subsequent to the productiou of this great fault, in what- 
ever portion of the missing series it took place, a great denuding 
force passed over the island, sweeping away the whole- of the uplifted 
rocks to the north of the fault, and reducing both its sides to the 
same uniform level. Of this long-continued period of denudation, we 
have additional evidence in various other parts of the island ; on Lang- 
ness, in the neighbourhood of Coshnahawin Head, etc., and particu- 
larly in the neighbourhood of Douglas Bay, where we have developed 
the uppermost beds of the clay-schists, containing fossils which iden- 
tify them with equivalent strata in other localities ; these show dis- 
tinctly marks of very extensive denudation. It is highly probable 
that the granite on the east side of Barrule was laid bare at that 
epoch, granitic pebbles appearing for the first time, so far as is known, 
in the Pleistocene gravels. That this denudation took place hefore 
the deposition of the Pleistocene beds, we have the most distinct 
proof in these beds resting in an undisturbed position along the line 
of the great fault. 
The superficial deposits of the Isle of Man are, in many respects, 
peculiarly well developed, and at the present time are remarkably in- 
teresting. We have first a very thick deposit of boulder-clay, con- 
taining numerous boulders of quartz, etc., occasionally of large size; 
this is succeeded by alternating beds of sand and gravel, enclosing 
enormous boulders of both native and foreign extraction. Connected 
with these beds are two series of remarkable low hills, one in the 
south of the island extending from the mouth of the Santon's Burn, 
in a south-west direction, towards the mountain-range, and the other, 
northerly, stretching " from Point Cranstal to Blue Head." Their 
general direction is almost parallel to the central range, and also to 
the direction of the glacial currents, as exhibited by the groovings 
and scratcliings in the underlying rocks. They consist of the clay, 
sand, and gravel of the Boulder formation, in the usual order : first, 
the clay of the colour of the underlying rocks, and containing frag- 
ments of them partially rounded ; then sandy gravel, much of which 
is of foreign origin ; and lastly, the Drift gravel, often enclosing large 
boulders of limestone, granite, etc. This order is well developed in 
the banks of the Silverburn, near the Creggans. Mount Strange, or 
Hango Hill, as it is more commonly called, at the head of Castletown 
Bay, is another interesting relic of the Boulder-clay formation. It 
rises about twenty feet above high-water, and consists of the Drift- 
clay enclosing numerous boulders of limestone, granite, quartz, etc., 
many of large size. I measured one, of dark-coloured limestone, 
probably from Derbyhaven, and found it almost three feet across each 
way. I also obtained from the clay at this spot, a number of shelly 
of the Boreal type, mostly in good preservation. This clift' is crowned 
with the ruins of the old place of execution, three fragments of the 
walls of which still remain, built of limestone, about a foot and a 
half thick. It is rapidly wasting away, and at the present rate a few 
