1909.] KECENT BIOLOGY OF SOME LIVING SHELLS. 765 



immediately pi^eceding the drift was that of the so-called ISTorwich 

 Crag. I hold, in fact, as I said previously, that there is no such 

 thing as a biological horizon represented by the drift beds of 

 Eastern England and Scotland ; that, whether distribvited by ice 

 or water, all their biological contents are older than themselve.s 

 and remanie. This is important in respect of the subject matter 

 of the present paper, since Mr. Lamplugh mentions that Mya 

 arenaria has been found in the lower Bridlington beds, although 

 he has not verified the discovery himself. 



In one instance I find Mya with a query cited from the drifts 

 of Lincolnshire (see Survey Memoirs, Line. p. 182). Mya arenaria 

 has been repeatedly reported as discovered in the drift beds of 

 Eastern England. Wood mentions it in ' The Crag Mollusca.' 

 It is named from Gorton by Mr. Harmer in his memoir on the 

 country round Norwich, and by Mr. Blake from Gorleston Olifi' in 

 his account of the country round Yarmouth and Lowestoft. The 

 comminvxted and water-worn condition of the fragments (whole 

 shells being very rare) makes it often uncertain about the identi- 

 fication of the species of Mya, since, as we have seen, it is only 

 the hinge that is of importance. Mr. Blake, speaking of Gorleston, 

 says : " Some of the loamy bands contained finely comminuted 

 shell-fragments, whereas in other places fragments from an inch to 

 more than two inches in length of such shells as Cyprina islandica 

 and Mya arenaria were seen mixed with smaller fragments, all 

 water- worn'"' (o/). cit. p. 39). It is clear that in view of Dr. Jensen's 

 discovery these fragments of M. arenaria should be re-examined. 

 What is plain, however, is that, whether they be true M. arenaria 

 or not, they have come from re-arranged Crag deposits and have 

 nothing to tell us of any horizon subsequent to the Crag. 



Let us now turn to the Irish Sea. It has always seemed to me 

 strange that^ the writers on the Crag beds should have so entirely 

 limited their investigations to the two sides of the southern part 

 of the North Sea. For it is quite clear that Britain in the time 

 of the Crag was washed by seas on the west as well as on the east 

 as it is now. It startled some people greatly when Jamieson 

 discovered true Crag deposits in Aberdeenshire as late as 1862, 

 and when similar deposits were discovered at St. Erth in Cornwall. 

 Now that we know that the fragmentary shells in the drift of 

 Eastern England are all derived from Crag beds, the problem has 

 become more interesting and important. 



It is at least a 2yrio?'i probable that wliat is true of the frag- 

 mentaiy shells in the drifts of Eastern England and Scotland is 

 true also of the broken shells of the drifts of Western England 

 and Scotland, and it has been generally urged that these broken 

 a,nd rubbed shell-fragments are also derivative. Those who know 

 them best are all of this opinion. In my ' Ice and Water ' I have 

 quoted Forbes, Mellard Read, Darbishire, Kendall, Crosskey, 

 G. Jeflfreys, and the British Association Committee on the beds of 

 Kintyre, for the drifts of Macclesfield, Lancashire, the Isle of 

 Man, Arran, and Kintyre {ojj. cit. ii. pp. 113-119). They are all 



