548 Frof. Harliness — On the Middle Pleistocene Deposits. 



Mr. Jamieson has also described the beds which yiehl shells in 

 Caithness.^ These beds, he states, consist of dark pebbly silt, or 

 stratified pebbly clay, or gritty mud, and they are generally suc- 

 ceeded by reddish brown stony clay, possessing the ordinary 

 characters of Boulder-clay. The strata in which the shelly frag- 

 ments are most abundant are sometimes seen resting on the Old Red 

 Sandstones, and the surfaces on which they repose frequently 

 exhibit well marked glacial striation. 



A list of shells, by Mr. Gwyn Jeffreys, is appended to Mr. 

 Jamieson's memoir, and this list contains seventy-five species. Few 

 of these shells are purely Arctic forms ; and, taking the molluscs col- 

 lectively from the Caithness beds, they exhibit a much less Arctic 

 facias than those from some other localities in Scotland, among which 

 is Gamrie. 



With reference to the strata in the west of Scotland which have 

 been so prolific in shells, and to which the attention of geologists 

 was first directed by the researches of the late Mr. Smith, of Jordan 

 Hill, these seem to possess very marked features which serve to 

 distinguish them from the shelly sands and gravels above alluded 

 to ; and these west of Scotland strata also appear to occur in a 

 different horizon. 



They are seen in the form of stratified beds which overlie the 

 Boulder-clay, and they never appear with Boulder-clay above them. 

 They bear about them, much more decidedly than the "Manure 

 gravels," or their British equivalents, the impress of an Arctic 

 climate. The west of Scotland shell-bearing strata belong to a more 

 recent portion of the Pleistocene period than the beds of England, 

 Wales, or Ireland, which contain shells and flint pebbles ; for a well 

 developed mass of Boulder-clay separates the two series from one 

 another. 



In England, the district which probably exhibits these shelly 

 sands and gravels, with flint pebbles, in the greatest perfection, is the 

 county of Norfolk ; and the relations of these strata to the deposits 

 above and below them in this county, have been well described by 

 Messrs. Prestwich, Searles Wood, jun., F. W. Harmer, and J. E. 

 Taylor. In some portions of this area, reposing upon the Norwich 

 Crags, are grey sands with quartzose and flint gravels, from which Mr. 

 Harmer has obtained, at Belaugh and Weybourne, a large number 

 of shells, amongst which Tellina solidula is specially abundant.- These 

 grey sands and gravels are succeeded by the lower Boulder-clay 

 (Brick-earth) containing travelled and striated blocks. The fauna of 

 this Boulder-clay is marked by an absence of all the mollusca of the 

 Crags, except such forms as are of an Arctic or Boreal type. In 

 position, this deposit seems to correspond with the Boulder-clay 

 underlying the shell-bearing beds at Howth. At Howth, however, 

 and elsewhere in Ireland, there have as j'et been discovered no de- 

 posits which can be correlated with the grey sands and gravels that 

 in Norfolk underlie the lower Boulder-clay. The lower Boulder- 



1 Quart. Journal of the Geol. Soc, Vol. xxii., p. 261, et seq. 

 2 Geological Magazine, Vol. VI., page 232. 



