1882.] 41 [Davis. 



where the supply of ground moraine was more than could be 

 carried forward by the ice ; a ledge of rock is sometimes found 

 below them, but not always, and does not seem essential; just 

 why they are placed where they are found does not yet appear. 

 They must have grown by gradual addition of material, preserv- 

 ing a form of least resistance to the on-flowing ice as they grew. 

 The rock-surface below them is, so far as I know, always glaciated, 

 showing that their accumulation was preceded by erosion, but 

 where the ice-sheet played such opposite roles, its erosion cannot 

 have been excessive. The thickness of the till in these clrumlins 

 is apparently due to their material having been gathered from a 

 much larger area than their base. 



L. Holmstrom supposes that the ground moraine moves slower than the 

 ice above it and thus serves as a protection to the rock below. (Neues 

 Jahrb. 1882, 58.) 



The'drumlins of Ireland are described by M. H. Close, who suggested 

 the application of this name to boulder-clay ridges ; he notes that they are 

 parallel to one another, and to the neighboring striae, although varying 

 greatly in direction in different districts, and thinks they " are the moraines 

 du fan d belonging to the ice flows that once covered the country." (Notes 

 on the General Glaciation of Ireland, Ireland Geol. Soc. Journ., i, 1866, 

 207-236. The map accompanying this paper is given also in Geol. Mag. 

 iv, 1877, 235.) Close adds later, "It is perfectly certain that it must have 

 been the rock-scoring agent which produced the boulder clay ridges." (The 

 Phys. Geol. of the Neighborhood of Dublin, Ireland Geol-. Soc. Journ., v, 

 1877-78,49. 



Kinahan and Close give an excellent map of the drumlins of a district of 

 Western Ireland, showing their remarkable parallelism to the glacial striae 

 in spite of their variable directions in different parts of the field ; they are 

 from half a mile to two miles long, and some are as much as 180 feet in 

 height. (General Glaciation of lar-Conn aught, Dublin, 1872.) 



Sir J. Hall called attention to the diluvial ridges in the neighborhood 

 of Edinboro' in his esssay on the Revolutions of the Earth's Surface. 

 (Edinb. Roy. Soc. Trans., vn, 1815, 175, etc.) 



J. Geikie mentions their occurrence in the Lowlands, as preserving with 

 small change the form given by the ice. (On Denudation in Scotland since 

 Glacial Times, Glasgow Geol. Soc. Trans., in, 1867, 59, 61, 68 ; and on 

 the Island of Lewis, Geol. Soc. Journ., xxix, 1873, 542.) He says later 

 that these long ridges, sowbacks or drums are parallel to one another, to 

 the valleys or straths in which they lie, and to the motion of the ice-sheet 

 under which they were moulded. (Great Ice Age, 1877, 13, 76.) 



