236 REPORT — 1887. 



to justify their immediate publication. On these, however, persevering 

 research may be expected, sooner or later, to throw a faller light. The 

 number of such ill-understood forms increases, I'ather than diminishes, 

 notwithstanding the success which has rewarded persevering inquiry in 

 the case of several such, and which encourages the hope that the con- 

 tinuance of such inquiries will be yet further rewarded in like manner. 



Fifteenth Report of the Committee, consisting of Professors J. 

 Prestwich, W. Boyd Dawkins, T. McK. Hughes, and T. Gr. 

 BoNNEY, Dr. H. W. Crosskey {Secretary), and Messrs. C. E. De 

 Eance, H. G-. FoRDHAM, D. Mackintosh, W. Pengelly, J. Plant, 

 and R. H. Tiddeman, appointpxl for the purpose of recording 

 the position, height above the sea, lithological characters, size, 

 and origin of the Erratic Blocks of England, Wales, and Ireland, 

 reporting other matters of interest connected with the same, 

 and talcing measures for their preservation. [Draivn up by Dr. 

 Crosskey, Seo-etary.) 



Mant details concerning erratic blocks not previously recorded have 

 been received by the Committee during the past year, which throw con- 

 siderable light on the important subject of their distribution. 



It is not the business of the Committee to enter upon theoretical 

 discussions. It may be useful, however, to point out a few of the salient 

 facts, established (in the opinion of the writer of this report) more and 

 more clearly by the researches undertaken by the Committee, and which 

 must be fully covered by any theory that may be adopted respecting the 

 Glacial epoch. 



1. Erratic blocks occur in groups as well as in isolated positions ; 

 and these groups have well-defined and distinctive characteristics, and 

 must not be confusedly mixed together. These groups sometimes contain 

 erratic blocks from one locality ; sometimes the blocks from various 

 localities are intermixed, but in either case they have characteristics as 

 distinct groups. 



2. The distribution of a considerable proportion of erratic blocks is 

 connected with the existing physical geography of Great Britain, as sub- 

 jected to elevation and depression during the Glacial epoch. The evidence 

 shows that many of them have travelled through the openings between 

 and among our present hills, and that they have been diverted from 

 their courses, or even blocked in their passage, by table-lands and emin- 

 ences. 



This fact, it must be noted, is at present stated with respect to a con- 

 siderable proportion, and not the whole of them. 



3. Erratic blocks have not all been distributed at one and the same time. 

 Their occurrence has been recorded in the reports, in four positions, viz. : 



(a) Beneath beds of clay, sand, and gravel. 



(6) Embedded in beds of clay, sand, and gravel, thickly or sparsely. 



(c) Resting upon beds of clay, sand, and gravel. 



(d) Resting upon the native rock of the district. 



It is clear that they could not have been deposited at the same time in all 

 these positions. 



