234 Correspondence. 



bed, no wonder we do not know them elsewhere in the gi-eat Bala (or 

 Caradoc) series. Besides that, in all probability, the north end of 

 the hill is made up of the Llandovery rocks. I will gage almost 

 anything I have (and that is not much), that the Llandovery con- 

 glomerates and shales occupy the hill of Pentre, and the slopes 

 above Tal-y-G-arth. Beyond this I will not suggest, for the neigh- 

 bouring ground looks terribly faulted ; and no one knows what is 

 the actual base of the Upper Silurian series in the valley, — seeing 

 that the pale "Tarannon" shales are not traced there, nor are the 

 Denbighshire grits : indeed the latter never were there at all. 



I know no place within easy reach, (for that is something in the 

 matter,) where a Club-meeting might do more good ; but then they 

 must make up their minds to walk the Mil across from north to south, 

 and in several directions ; and not disperse their energies over a long 

 section, or go in search of the picturesque. The geology is very 

 simple in the hill itself; but outside of it, faults and unconformable 

 junctions obscure everything. 



1. Slates under the lower limestone. 



2. Lower limestone (Bala). 



3. Slates between the limestones (Upper Bala). 



4. Hirnant limestone ? 



5. Soft slates — which may be Llandovery ? 



6. Llandovery conglomerates ? 



Will anybody set to work on it ? J. W. Saltek. 



GENERAL GLACIATION OF IRELAND. 



(WITH A MAP.) 



To the Editor of the Geological Magazine. 



Sir, — A number of copies of the accompanying map having been 

 cast adrift by the unforeseen discontinuation of the Dublin Quarterly 

 Journal of Science, for which they had been prepared, you have 

 charitably consented to afford them harbour in the Gtbological 

 Magazine. At your desire I give an explanation of the map, and a 

 concise account of the paper which it illustrates (noticed by yourself 

 in your April number, and to be contained in the forthcoming part 

 of the Journal of the Eoyal Geological Society of Ireland). The 

 facts have been derived from a variety of sources, including my own 

 observation. 



The black strokes give the direction of the parallel ridging, which 

 is so well developed over much of the low ground in this country. 

 The ridges usually consist of Boulder-clay with well scratched and 

 blunted (not rolled) stones; but sometimes the parallel shaping 

 seems to be partially wrought in the rock. The Boulder-clay ridges 

 are totally distinct from Eskers (or Kames) ; their average length is 

 about three quarters of a mile ; they sometimes exceed one hundred 

 feet in height. The red strokes represent parallel rock-scorings. 

 When the scorings show clearly, of themselves, which way the 

 grinding agent went along the line of its motion, the strokes repre- 

 senting them are made into arrows. Cross striations, later than the 



