GSINDLET — GEOLOGY Or THE ISLE OE MAIS'. 



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great, as it includes tlie whole of tlie Manx Carboniferous series, the 

 Devonian conglomerate, and a considerable portion of the underlying- 

 schists. Subsequent to the production 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 

 tlie 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 Craustal 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 scratchings in the underlying rocks. They consist of the clay, 

 sand, and gravel of the Boulder formation, in the usual order : first, 

 the cla_Y 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 shells 

 of the Boreal type, mostly in good preservation. This cliflT 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 



