John Home — Newer Deposits of the hie of Man. 329 



country. Or the high-lands may have been enveloped in ice, and 

 from the margins thereof, rock detritus may have been dropped into 

 the sea, forming drift accumulations, not, however, normal glacial 

 drift, as the detritus would have been more or less washed and 

 re-arranged by marine action. 



As to the Irish drift. Over twenty years ago, it was supposed that 

 there were two glacial drifts separated by gravels and sands ; but 

 during the subsequent examination of the island under the late 

 J. Beete Jukes, F.R.S., it was proved, that although there are two 

 glacial drifts (boulder-clay drift and boulder or moraine drift), yet 

 between them there are no sands and gravels, the sands and gravels 

 being newer than both, and found indiscriminately on either. 

 Within the last few years, however, on very partial and immature 

 observations, this old theory of the " middle gravels " was again 

 started ; but in subsequent papers the unsoundness of the arguments 

 and statements in its favour was demonstrated. If the author of 

 the paper on the " Post-Pliocene Formation of the Isle of Man " will 

 turn to my letter in the April Number of the Magazine, he will find 

 that inadvertently he misquotes it. A glacial drift above the 

 " middle gravels " is what has not been found in Ireland, but an 

 upper glacial drift is well known. 



IX. — The Post-Pliocene Formations oe the Isle op Man. 



By John Horne, F.G.S. ; 



Of the Geological Survey of Scotland. 



IN the postscript to his paper on the Post -Pliocene Formations 

 of the Isle of Man, Mr. J. A. Birds takes exception to my 

 classification of the Manx drifts. 1 He states that, " a priori, is it not 

 against Mr. Home's view of his Lower Boulder-clay being really 

 such that there should be intermediate formations of sand and gravel 

 when the cold was at its extreme, and the ice, according to his 

 showing, from 2000 to 3000 feet thick?" To those who are well 

 acquainted with the appearances presented by interglacial deposits, 

 this objection cannot have any weight. The Lower Boulder-clay 

 or Till of North America, of Sweden, and of Scotland, contains well- 

 marked accumulations of fossiliferous sedimentary matter ; and non- 

 fossiliferous sand and gravel are of common occurrence in the Till 

 of these and other countries. From these and other considerations, 

 it is most probable that the Till or Lower Boulder-clay and its inter- 

 calated beds betoken a succession of cold and warm periods. The 

 appearance of layers of sand and gravel in the Manx Boulder-clay 

 is quite in keeping with the facts referred to. 



Mr. Birds further notes, " that if all the deposits are assigned to 

 the first glacial period and the great submergence, what memorials 

 are left, beyond some possible moraines, of the second glacial period, 

 or the times next preceding and following it ? Surely there ought to 

 be such if the land has not been submerged since." The author 

 seems to forget that the glaciers of the post-submergence period 

 were confined mainly to the upland valleys. They did not deploy 

 1 See Geol. Mag. May, 1875, p. 226. 



