330 John Home — Newer Deposits of the Isle of Man. 



far into the low grounds, and therefore no other memorials could 

 have been left, except " some possible moraines." 



One or two remarks may now be made on the succession advanced 

 by Mr. Birds. He considers the true Lower Boulder-clay to be 

 represented by the shelly clays which occur in the cliff sections in 

 the north part of the island, stretching from Bamsey to the Point of 

 Ayre, and thence to Kirkmichael. Forbes long ago examined these 

 beds, and pointed out that they lie usually at the base of the cliffs, 

 being capped by a great thickness of stratified sands and gravels, on 

 which rest large boulders. Now the difference between these shelly 

 clays and true Lower Boulder-clay is so distinct and obvious that I 

 cannot see how any one who has had experience in mapping drifts 

 can possibly confound them. The clays, which attain a great thick- 

 ness between Sea-view and Port Cranstal, contain few stones. These 

 are no doubt smoothed, and often scratched ; but their occurrence is 

 quite exceptional. Moreover, the clays are often finely laminated, 

 and the position of the stones in some places is such as to lead one 

 to believe that they had been dropped during the accumulation of 

 the thin layers of mud. In short, these marls, so far as I saw, 

 strongly resemble in general appearance the glacial clays of the 

 Forth and Clyde basins, and similar deposits at Dumfries in the 

 Nith basin. It is hardly necessary to point out that such is not the 

 character of true Lower Boulder-clay or Till. This latter deposit 

 is always highly charged with stones, most of which are scratched on 

 every side, the matrix being extremely tough and quite devoid of 

 stratification. But further, these marls, north of Ramsey, contain 

 shells in abundance, which have been named by Forbes ; while the 

 true Lower Boulder-clay is unfossiliferous. It is quite true that 

 shells have been obtained from Boulder-clays in different parts of 

 Scotland, Lancashire, and elsewhere ; but these are more recent than 

 the Till, though belonging to the pre-subergence period. If further 

 proof Were needed to convince Mr. Birds that there is a difference 

 between these shelly clays and true Boulder-clay, reference might 

 be made to a section near Port St. Mary, on the south side of the 

 island. After turning the point south of the lime-kilns, a deposit of 

 stiff stony clay, packed with angular, subangular, and smoothed 

 stones, most of them scratched, is found resting on striated beds of 

 Carboniferous Limestone. This bed, which resembles an Upper 

 Boulder-clay, is overlaid by finely laminated Brick-clay with shells, 

 but containing few stones, from 8ft. to 10ft. thick; while the shelly 

 clay is capped in turn by stratified Sands and Gravels. There can 

 be little doubt that this shelly clay is of the same age as the marls 

 north of Bamsey, and, if so, then there is here direct evidence that 

 the shelly clays are more recent than the Upper Boulder-clay. 



Again, Mr. Birds ranks all the Boulder-clays, other than the 

 shelly clays, as belonging to his upper series. " This Upper 

 Boulder-clay," says the author, " was not formed altogether during 

 the second continental period, but probably it was deposited during 

 the middle or towards the latter end of the emergence, and continued 

 to be deposited for some time during the second submergence." 1 

 1 See Geol. Mag. Feb. 1875, p. 82, et seq. 



