170 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



drift in that part impossible until the crest of this scarp had become 

 submerged, until which event the set of the current must have 

 been either east or else west along the shore formed by the scarp 

 itseK. If, as can scarcely be doubted, the chalk, so profuse in the 

 basement clay of Holderness, and tolerably abundant in the lower 

 part of the purple clay of Holderness (a district lying east and south- 

 east of the Wold), was derived from the high part of the Wold 

 country which was then above water, and if free water existed 

 over the equally low part beneath the northern scarp at Speeton, 

 while the scarp ranges westwards from that place up to elevations 

 of 800 feet, how can we suppose this low part to have escaped the 

 chalk debris, if these relative elevations, or anything like them, had 

 then come into existence ? Purther the scarp trends from Speeton 

 in a north-westerly direction, past Hunmanby to Folkton ; and it is 

 precisely in such a direction that the blocks of Shap granite, not 

 unfrequent in this clay, have come. Again, there is a similar 

 absence of chalk debris in the purple clay that occupies the vale of 

 York at Gate Helmsley, from near which place the Wold-scarp runs 

 north-eastwards for 30 miles at extreme elevations, as well as a 

 similar absence of the basement clay ; but it is in the same direction 

 as that in which Gate Helmsley hes, relatively to the north part of 

 the Wolds, that the chalky Glacial clay stretches to North Warwick- 

 shire ; so that if the chalk that forms the principal ingredient of the 

 Glacial clay of that part were derived from any point south of 

 the north-western angle of the Wolds, it would involve a still 

 less southerly direction of the drift than that which would strike 

 Gate Helmsley. Further, the chalkless* purple clay of the south 

 side of Plamborough Head, shown in fig. 1 to rest on the beds of 

 chalk-debris c, is at as low a level as that at Speeton Wold-foot, but 

 5 miles south of it, and therefore quite within the set of any such 

 supposed soutlierly drift. Finally, there is the case of the lead- 

 coloured sediment of which the basement clay is composed. This 

 clay, from its exposure at Kilnsea, in the south of Holderness, to 

 Skipsea, in the north of it, is quite homogeneous, and similar to 

 that which stretches to the Thames heights and to Warwickshire. 

 If, however, the Glacial-clay sediment were deposited under the 

 conditions of such an undeviating southerly drift as supposed, how 

 are we to explain the absence of this leaden-coloured sediment 

 everywhere to the north of Skipsea ? It is clear that it could not 

 be supplied by the chalk Wold which intervenes between that place 

 and Speeton ; and yet, over all this intervening part, as well as at 

 Speeton, and thence northward, the Glacial clay is composed exclu- 

 sively of the purplish-brown sediment which forms the clay (c) that 

 rests upon the basement clay («) further south ; while still further 

 south, at Grimsby, we get, by overlap, the purple clay (c) again rest- 

 ing directly on the chalk. 



* There may not be an absolutely complete absence of chalk here ; but it is 

 sufficiently so to be in total contrast to the basement clay of Holderness, not 

 many miles to the southward, while it is in intimate resemblance to the upper 

 part of the purple clay that caps this basement clay along the coast. 



