GLACIAL BEDS. 499 



mud ; and then the whole was subjected to some disturbing force — ice in some 

 form — which removed it piecemeal, perhaps in frozen masses.' 



The Molluscan fauna of the Bridlington Crag is essentially Arctic in character. 

 The species include Saxicava ritgosa, Pecten Islandiciis, Pectuncidus glyciineris, 

 Cardiiim Islaiidicum, C. Grcenlaitdiciun, Nucida Cobboldiiv, Cyprina Islandicuy 

 Astarte horealis, A. depressa, Tellina Balthica, Scalaria Grcenlandica, Biiccitium 

 tindatiim, Trophon scalariformis [clathratns), etc. ; also RhyncJionella psittacca? 

 Foraminifera and Ostracoda have been determined, as well as a few Cirripedes. 

 Some Vertebrata occur, which have been derived from Crag, Eocene, and older 

 strata. 



Beds of laminated clay, bedded loam and sand from 4 to 20 feet thick, 

 occasionally intervene between the Basement Clay and overlying Purple Clay ; and 

 the latter appears in some places to be stratified.-* 



Overlying this Basement Clay, there are in Yorkshire beds of a purplish-brown 

 colour termed the 'Purple clay' by Mr. S. V. Wood, jun., and the Rev. J. L. 

 Rome.* This clay has the most extensive development of any bed superior to the 

 Chalk in this county, not only overlapping the Basement clay in all directions, but 

 extending far beyond the north scarp of the Wolds in an irregular belt along the 

 coast northwards. In its lower portion it abounds with boulders of older 

 Secondary, Palceozoic, and Metamorphic rocks, and in Holderness it contains 

 considerable quantities of Chalk. 



The Lower Purple Clay is described by Mr. Reid as a tough lead-coloured or 

 purplish-blue Boulder Clay, generally very chalky near the base, but less so in the 

 upper part. It contains shell-fragments and many scratched boulders. 



The Upper Purple Clay is very similar to the Lower, but contains few shell- 

 fragments. It includes the ' Purple Boulder Clay without Chalk ' of Mr. Wood. 

 The two Clays are sometimes separated by a few feet of gravel, or by a "red 

 band " of reconstructed Boulder Clay. Above the Upper Purple Clay there occurs, 

 in places, stratified sub-angular gravel, which is thicker and more persistent 

 than the lower beds of gravel ; it was termed the Hessle Gravel by Messrs. Wood 

 and Rome, from Hessle, west of Hull, and is probably distinct from the mamma- 

 liferous gravel of Hessle, and the marine gravel of Kelsey Hill. Upon this gravel 

 rests the Hessle Clay of Mr. Wood. This Clay, sometimes known as the ' Brown 

 Clay,'* is not distinguishable, when unweathered, from the Purple Clays, 

 though the boulders are generally smaller and less abundant, and shell-fragments, 

 rare in the Upper Purple Clay, have not yet been found in the Hessle Clay. 

 Indeed, Mr. Reid states that the three Boulder Clays are so much alike, that, 

 without continuous sections, it is imp.ossible to say to which division an isolated 

 exposure belongs.'' The beds of Boulder Clay vary from 10 to 40 feet in thickness, 

 and the total thickness of the Drifts is upwards of 100 feet. 



Hessle and Kelsey Hill Beds. — Inland at Hessle remains o^ Elephas primigenhis. 

 Rhinoceros, etc., have been found in gravel and sand beneath Boulder Clay. The 

 precise age of the deposit is not fixed ; it rests on Chalk, and is overlaid by 

 Boulder Clay, but that Drift cannot be correlated with any particular division of 

 the Boulder Clay exhibited on the Holderness coast, though undoubtedly it 

 belongs to the series. According to Mr. Reid this mammaliferous deposit is 

 probably older than the so-called Hessle gravel of Messrs. Wood and Rome, seen 

 on the coast between the Upper Purple Clay and the Hessle Clay. At Kelsey 

 Hill near Hedon, and other places near Hull, there is a deposit of gravel containing 

 fragments of marine shells, Purpura lapillns, Buccinum undatiim, Ostrea ednlis, 

 Cardiuin edule, Cyprina Islandica, Tellina Balthica, etc. ; and also Corbicula 

 flumiimlis, Elephas prirnigenius, and Rhinoceros. The gravel is upwards of 60 feet 

 thick at Kelsey Hill, and it is underlaid and overlaid by Boulder Clay. The land 



1 Q J. xxxvi. 515. 



* S. P. Woodward, G. Mag. 1864, p. 49 ; C. Reid, Geol. Holderness, p. 22. 

 3 See also J. R. Dakyns, G. Mag. 1879, p. 528. 



* Q. J. xxiv. 184. 



5 See also Whewell, Proc. G. S. ii. 63S, iii. 83. 



* Geol. Holderness, p. 27. 



