Correspondence — Mr. J. A. Birds. 429 



one of the intercalated beds with sand and gravel, they might at least 

 easily be a portion, probably a lower portion, of the Middle sands and 

 gravels, and so still the lowest Post-Pliocene formations in the 

 island. 



It seems, from what I have learnt from Mr. Home's and Mr. 

 Kinahan's papers, as if there was a different division of the glacial 

 series recognized by some geologists in Scotland and Ireland, from 

 that adopted by the Geological Survey for the north-west of England ; 

 the former consisting: of 



1. Lower Boulder-clay. 



2. Upper or Moraine Boulder-drift. 



3. Kame or Esker Drift. 1 



the latter of 



1. Lower Boulder-clay. 



2. Middle Sands and Gravels. 



3. Upper Boulder-clay. 



and it would certainly be a point of some interest to determine to 

 which order, or if to either, the Post- Pliocene deposits of the Isle of 

 Man conform. But I think this must be decided by stronger evidence 

 than that of the section at the southern end of the island to which 

 Mr. Home refers, and with regard to which his words admit of a 

 double doubt — first, whether the underlying formation is really an 

 Upper Boulder-clay, and not a Lower ; and secondly, whether the clay 

 with shells there is certainly identical with the shelly clay in the north. 

 It must be decided, if not by direct evidence of superposition, at 

 least by further probable evidence of such superposition, and also, 

 as far as possible, by that of Molluscan contents. Do the shells of 

 the Isle of Man deposits resemble more those of the Blackpool Middle 

 sands and gravels, or those of the Clyde and Forth basins (of a more 

 Arctic 2 character), with which Mr. Home identifies these beds ? With 

 regard to Mr. Home's lithographed section, it seemed to me, though 

 on slight evidence, when on the spot, rather as if the red clay of the 

 north of the island, in the bed of the Ballure stream, passed under 

 the clays and gravels which the lithograph represents as Lower 

 Glacial. 



In answer to Mr. Kinahan, I need only say that I have used the 

 term " Glacial Drift " in the sense in which I find it used (or at least 

 language which implies such a use of it), by the highest authorities 

 from Forbes till now, that is, of Drift formed whether by ice alone, 

 or by ice and sea together {i.e. Marine Glacial Drift), during the 

 Glacial Epoch. No doubt much glacial drift in all ages, including 

 that of its first formation, has been reconstructed in the manner 

 explained by Mr. Kinahan, but, with deference to him, it is difficult 

 to believe that extensive deposits like the Middle sands and gravels, 

 and the Upper Boulder-clay (in Lancashire and Cheshire), have alto- 

 gether or chiefly, been formed in this way. These would still seem 



1 Mr. Kinahan and Mr. Home identify these with the Middle or " Marine " 

 (Irish) gravels, though I had been led to believe that the difference between them 

 was sufficiently marked by the presence of shells and chalk- flints in the latter, and 

 their almost entire absence in the former. (See. Geol. Mag. Dec. 1869, p. 544.) 



2 See Geol. Mag. Dec. 1869, p. 548. 



