298 E. Hull — General Relations of the Drift Deposits. 



there can be no doubt that they are for the most part formed of the 

 Limestone Gravel or Middle Drift, in some places re-modelled, but in 

 others apparently retaining its original form of stratification.^ One 

 of these boulders, resting on the flanks of an Esker near Durrow, 

 called the " Pilgrims' Eoad Esker," formed of limestone, was found 

 by Mr. J. O'Kelly, of the G-eological Survey, to measure 18 by 15 

 by 12 feet.^ Generally these boulders are to be found in such 

 positions ; and though I was for a time at a loss to account for their 

 presence, I venture to suggest that they are the monuments of the 

 former existence of a formation, viz., the Upper Boulder-clay, of 

 which the soft and fine materials have been swept away, while the 

 large boulders it once held imbedded have resisted the agencies of 

 destruction, and remain behind stranded on the Eskers. As a 

 parallel case, I may refer to the presence of the " Sarsen stones," or 

 " Grey wethers," on the Chalk Downs of Wilts and Berks, relics of 

 the Tertiary strata in which they were once imbedded, but of which 

 there are frequently no traces in the immediate neighbourhood of the 

 " Sarsen stones " themselves. 



Varying levels of the Drift deposits. — The Limestone Gravel of 

 the neighbourhood of Dublin has been traced to considerable eleva- 

 tions on the flanks of the Dublin and Wicklow Hills, by the 

 Eev. Maxwell Close, Mr. Wyley, late of the Geological Survey, Dr. 

 Scouler, and others. These elevations reach 1,200 and 1,235 feet on 

 Montpelier Hill;^ and as the gravels contain fragments of shells, 

 these levels undoubtedly indicate the amount of depression of the 

 land below its present level during the Middle Glacial stage. 



These observations are in accordance with those I made very care- 

 fully in Lancashire,* where I found each member of the Drift to rise 

 gradually towards the hills, and sink down under the plains. The 

 position, therefore, which the Drift deposits assume, is not that of 

 horizontal terraces, occupying successive levels as we ascend the 

 sides of the hills (a very prevalent view of the subject), bat one in 

 which the difierent members accommodate themselves to the original 

 form of the ground, rising and cropping out in succession at certain 

 elevations, depending on the amount of denudation to which they 

 have been subjected. This arrangement is illustrated in some degree 

 by the section along the coast at Killiney and Bally brack (see Fig. 1), 

 where the beds are seen to slope (or dip) down from Killiney Hill 

 into the plain below. 



General Conclusions. — The division of the Glacial period into three 

 stages, first clearly demonstrated by Professor Eamsay, in 1852, 

 when treating on the Glacial phenomena of North Wales,^ marked by 

 corresponding deposits over the three kingdoms, is one which I think 

 may now be regarded as fully established, and is an immense advance 

 on our knowledge as compared with that a quarter of a century since. 

 (3) The earliest stage was one of general elevation of the land and sea- 



' See account of the Eskers at Stonepark by Mr. Symes, F.G.S., of the Geological 

 Survey. Explanatory Memoir, Sheets 86, 87, and pp. 49-61, with woodcut. 



2 Explanation Sheets 98, 29, and p. 27. 



3 Explanation Sheets 102 and 112. Geol. Survey Maps, p. 67. 

 * " Drift Deposits of Manchester," supra cit. pp. 457-8. 



5 Quart. Journ. Geol. Soc, vol. viii. 



