766 on THE RECENT BIOLOGY OF SOME LIVING SHELLS. [Nov. 9, 



agreed on the subject that these fragmentary shells are trans- 

 ported, re-arranged and derived from earlier beds. ISfow the beds 

 pi^eceding the drift in Western England, just as in Eastern 

 England, must have been deposited in the Crag sea. The shells 

 are no doubt not precisely the same on both sides of England, 

 bvit the conditions were not quite the same either. It is ex- 

 ceedingly probable that Ireland and Scotland were united at some 

 point during the Crag time, so that the shells in the southern 

 part of the Irish Sea and those in the northern part would have 

 been somewhat difi'erent, there being no access in the south to the 

 northern indraft of cold water. This would not affect the con- 

 temporaneousness of the shell-beds, however, on either side of the 

 island any moi-e than the present divergent fauna of the Baltic 

 and the Cattegat do so. 



While the contents of the drift beds show every sign of being 

 derivative, this does not mean that a,ll the later beds in the 

 western parts of Great Britain are so. Just as there is every 

 reason for thinking the shell-beds in Nairnshire to be in situ and 

 to be, as I have urged elsewhere, older than the drift which over- 

 lies them (see op. cit. ii. p. 118), so also is it the case with the low- 

 lying shell-beds in the Kyles of Bute and some other sites in 

 Western Scotland. Mr. James Smith, of Jordan Hill, was the 

 first to disci'iminate two sets of shell -beds in this district (see 

 Smith, ' Newer PHocene Geology,' p. 79). These seem certainly 

 in situ and to be older also than the drift, and in my opinion 

 they represent the later Crag of the West Sea just as the beds 

 at Aberdeen represent the Crag of the North Sea. 



Here again our shell Mya arenca-ia comes to our assistance. 

 Just as it abounds in the Norwich Crag so does it abound also in 

 the Bute beds. 



Two splendid valves of typical Mya arenaria from the shell-beds 

 of the Kyles of Bute are in the British Museum from the Richmond 

 Collection, and are labelled Glacial (see number 35020). 



Crosskey and Robertson found the shell in the same place. 

 They in fact presented some specimens of it from the Kyles of 

 Bute to Professor Sars in 1866. Brogger describes them as of the 

 typical form and they still preserve their original label, Ilya 

 arenaria, glacial clays, Kyles of Bute. To which Sars added in 

 his own handwriting, " glacial " with a query. The shell is 

 named from the same locality in the appendix to Sir A. Geikie's 

 Memoir on the Glacial Drift of Scotland (Trans. Geol. Soc. Glas. 

 i. pt. 2, p. 176). 



Robertson and Crosskey also name a single valve of Mya aren- 

 aria as having been found in the Lochgilp beds {ibid. iii. p. 122). 

 These several beds I deem to be what are generally called pre-glacial 

 or, as I prefer to call them, late Crag ; and it was from similar 

 late Crag beds that the fragmentary shells in the Isle of Man aiid 

 the Lancashire drifts were derived and among them the Mya 

 arenaria, which is mentioned from the Isle of Man beds at Glen 

 Wyllin by Mr. Kendall. 



