66 S. V. Wood, Jun. — Sequence of the Glacial Beds. 



the presence of many arctic shells, are all, or nearly all, of the same 

 later age, and belong, some to the series e", e, and e, and the rest 

 to the earlier part of the still later stage, which, for convenience, 

 I call Post-glacial,^ that is, to the period of the great emergence, or 

 to the earlier part of that which succeeded it in the north, such as 

 the beds b and c.^ 



The Caithness beds, brought also by Mr. Harkness into identity with 

 the East Anglian Middle Glacial, seem to offer no points whatever to 

 support any such conclusion. It is the opinion of their latest descri- 

 ber, Mr. Jamieson,^ that, while they contain a mixture of species from 

 Glacial beds of earlier and later date, they belong all of them to the 

 later part of the Scotch series ; and, assuredly, there is nothing in the 

 fauna yet described from them which would admit of their being re- 

 garded as of similar age to that bed, described in 1860, as Crag, which 

 seems to me to be the Middle Glacial. 



As I propose, at a future time, to endeavour to show the grounds 

 for this opinion as to the relatively newer age of most of the Scotch 

 beds, I shall not allude further to them here than to observe that in 

 none of the Scotch beds, except that of Aberdeenshire, before referred 

 to, which contains one of them, have there yet occurred such shells 

 as the well-known Crag forms — Tellina pretenuis, Tellina ohliqua, 

 Cardita scalaris, and Nucula Gohholdice. Of these, Tellina pretenuis 

 occurs in the East Anglian Lower Glacial. Tellina ohliqua occurs 

 in the same, and also in the Middle Glacial, and at Bridlington. 

 Cardita scalaris occurs in the Middle Glacial, and Nucula Cobboldice 

 both in the Lower Glacial and in the Upper (Bridlington). 



All these four shells were, until recently, regarded as extinct. 

 The two first are still unknown living. Cardita scalaris has 

 recently been identified, by my father, with Cardita ventricosa of 

 Gould, from the American North Pacific coast, and Nucula Cobholdioe 

 is either extinct or else identical with another Pacific shell, Nucula 

 Lynlli. 



With those who attach more importance to a list of shells simpliciter 

 than I am disposed to do, these shells should have much weight ; for 

 though Tellina ohliqua, regarded by most paleeontologists as a species, 

 was looked upon only as a variety of Tellina calcarea {proxima or lata) 

 by Edwrrd Forbes, and described as a synonym of that shell in Forbes 

 and Hanley's Mollusca, — a view lately adopted also by Mr. Jeffreys, — 

 it is unknown living. Whether a variety or a species, however (and 

 these terms appear to me matters of degree and not of kind), the 

 shell is of equal, and indeed, from its abundance in most deposits 

 where it exists, of greater, geological value than most so-called 

 species ; for it is one of the best marked types of the upper Crag 

 occurring in the newer part of that formation, the Chillesford, in 



1 It will have appeared from the earlier part of this paper that I use the term 

 Fost-gldcial in a very different sense from that in which it is used by the Scotch 

 Geologists. 



2 This seems also to have been in some degree the opinion of the late Dr. "Wood- 

 ward, judging from the last five lines of his paper on the Bridlington fauna. Geol. 

 Mag., Vol. 1., p. 62. 



3 Quart. Journ., vol. xxii., p. 280. 



