82 J. A. Birds — On the Isle of Man. 



4thly. A second submergence, attended probably with many oscil- 

 lations, until St. George's and the English Channels were formed, 

 and the British Isles at length assumed their present shape. 



I am not aware whether this hypothetical history — which, until 

 some more satisfactory theory is suggested, must be assumed as the 

 basis of all reasoning upon the Post-pliocene Formations — originally 

 led to their threefold division into an Upper Boulder-clay, a Middle 

 Drift of sand and gravel, and a Lower Boulder-clay, corresponding 

 to, and by some supposed to be the product of the first three periods ; 

 but it seems not improbable. 



However this may be, the division now appears to be fully 

 supported by facts, and it only requires some modification in the 

 reference of the several members to their respective periods of for- 

 mation to render it, apparently, satisfactory. 



Thus, instead of assuming that the Lower Boulder-clay corresponds 

 to and was entirely formed by land-ice during the first continental 

 period, we believe that the materials of it were then ground up by 

 land-ice and subsequently deposited in the sea, from the time when 

 the land began to sink until perhaps the middle of the period of sub- 

 mergence. 



Again, the Upper Boulder-clay 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 ; the 

 interval between the middle of the first submergence and that of 

 emergence being one in which a temperate climate prevailed and no 

 glacial deposits were formed. The simple diagrams given on page 



83 will illustrate my meaning at a glance. 



Now to apply the above explanation to the glacial deposits of the 

 Isle of Man. The whole northern portion, about a third of the 

 island, north of the road from Bamsey to Kirk-Michael, is occupied 

 by the Lower Boulder-clay and Middle Drift sands and gravel. It 

 is best seen in the cliffs from Sea-view to Port Cranstal, at the 

 eastern end of the Bride Hills, and again at the western end of the 

 little chain at Blue Point. The sections are very similar, and con- 

 sist of stratified yellow sand and gravel at the top, averaging 10 to 

 15 feet, succeeded by a great depth of brown clay, interspersed with 

 patches of sand, and. here and there a bed of gravel, and the whole 

 attaining a maximum thickness, at Point Cranstal, of from 100 to 

 150 feet. The clay contains but few stones. The gravel-beds consist 

 chiefly of local schist and quartz, with a very lai'ge admixture of 

 stones foreign to the island — Permian rocks, chalk flints, granites, 

 syenites, traps, porphyries, etc. The largest accumulation of pebbles 

 from these beds is round the Point of Ayre, where the beach at low 

 water, for a distance of nearly two miles, is composed of several 

 terraces of shingle, apparently of considerable depth, and having a 

 total width of 80 to 100 feet. Searching along this shore I found, 

 besides the flints above mentioned, which must have come from the 

 north-east of Ireland, a very great variety of granites, syenites, etc., 

 probably part from Ireland, and part from the south of Scotland, 



