WOOD AND ROIVTE — LTNCOLXSHTRK ANTD S.E. YORK>!IfTRE. 149 



which we have traced it ; but we have only examined it systematically 

 as far as Scarborough, to which place the coast-belt of it is continu- 

 ous. The distinction of this clay from the basement clay becomes 

 very marked where it rests on the chalk Wold, as around Flam- 

 borough and Speeton, since none of the intermediate features which 

 characterize its base where it rests on the basement clay exist in 

 this part, no chalk at all appearing in it north of Plamborough. 

 The basement clay occurs only on the eastern and southern side 

 of the Yorkshire Wold, and is there mostly below the beach-line ; 

 but the purple clay not only has a place on both sides of the chalk 

 escarpment, but at Speeton envelopes it, occurring on the summit 

 under Speeton at an elevation exceeding 400 feet. The fortunate 

 circumstance, that the very narrow belt of purple clay which has 

 escaped denudation occurs on the coast, thus permits of the condition 

 of the chalk escarpment prior to the purple-clay deposit being seen ; 

 for with this exception the whole of the Wold has been completely 

 denuded of it. The fact that this clay envelopes the north scarp 

 and lies also at its foot, while the basement clay is wholly absent 

 from both positions, is one of great importance in reference to the 

 sequence of the events which followed the commencement of the 

 Glacial period. The purple clay alone seems present beneath the 

 Hessle clay in north-east Lincolnshire, while further to the south, 

 by Burgh, the basement clay ap^jears (from a boring mentioned in 

 the Appendix) to occur. The purple clay in its lower part abounds 

 in boulders, being in fact quite dotted with small angular frag- 

 ments of older Secondary, of Palseozoic, and of metamorphic rocks. 

 These small fragments just take the place of the small chalk debris of 

 the basement clay and its correlative deposit, the Upper Glacial clay of 

 the more southern counties. It is in the same lower portion of the 

 purple clay also that the great blocks most abundantly occur. In the 

 upper portion the small fragments gradually disappear, and the large 

 blocks also become far less frequent, so that the uppermost part 

 (which at DimHngton can be well contrasted with the lower) is 

 scarcely entitled to the distinction of " Boulder-clay." The lower part 

 of the purple clay in Holderness also contains some chalk, but gene- 

 rally in small quantities only ; so that we may infer that the portion 

 resting on the Wolds and that which stretches northwards from the 

 Wold-foot at Speeton, which is destitute altogether of chalk, belong 

 only to the upper part of this formation*. Interspersed in the 

 lower and central parts of the purple clay, where the older Secondary, 

 Palaeozoic, and metamorphic fragments as well as the large blocks 

 abound, are some beds of sand with gravels. They are of very 

 limited extent and very intermittent. It is from one of these, just 

 about the beach-line, and at a vertical distance, judging from the 

 boring in Bridlington harbour mentioned by Young and Bird, of some 

 40 feet from the base of the purple clay (including in that term the 

 beds b as the base of that clay), that the moUusca first made known 

 by Mr. Bean, and long known as those of the "Bridlington Crag," 

 were, and still occasionally are, procured. The position of the bed 

 * The reasons for this inference are fully discussed further on, pp. 168-170. 



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