398 G. W. Lamplugh — The Boulder-clay at Bridlington. 



As I was unable to find any trace of the freshwater beds in the 

 cliff-section, it is difficult to make out their true relation to the beds 

 beneath, which were sometimes the lowest part of the Purple (which 

 has been almost altogether denuded away here), and sometimes the 

 " Basement " Clay. It is somewhat curious that just over the extent 

 covered by these remnants, the Middle Laminated clay should be 

 absent ; but as it is also absent at other places, this may be merely a 

 coincidence. 



The way in which the freshwater beds were tilted and cut up 

 into shreds, separated from each other by thick walls of Boulder- 

 clay, was remarkable. One long strip, containing shells, was five 

 yards long, by only three inches in width, and had gravel on each side. 

 In another case, a small patch of peat, one foot square, was bounded 

 on all sides by Boulder-clay, and was, to all intents and purposes, 

 a boulder itself. These ' shreds and patches ' were spread here and 

 there over the whole extent of the peculiar clay just described. 



To all appearances, we have here the silt of an old pond, of limited 

 extent, and interglacial in age, through which the ice, on its return, 

 has ploughed, partially destroying it. 



As to the exact place of this interglacial period in the series, as 

 seen in the cliff, there is some doubt. It was, at any rate, later 

 than the pause which took place between the formation of the 

 " Basement " and " Purple " clays ; and of which the Middle Laminated 

 band is a record. But whether it was formed during a local pause 

 in the Purple clay period itself, or was altogether later, it is a more 

 difficult matter to determine. 



It is probable, from the many included sand and gravel beds in 

 the " Purple " clay, that changes of some sort did take place during 

 its formation, but, as far as is known, these sand beds contain no 

 signs of life, either freshwater or marine. 



If we allow that it was of later age than the Purple clay, we 

 must also grant that the peculiar clay already described, with which 

 it is mingled, and by which it is in part covered, is not merely 

 the upper part of the Purple clay, but is altogether newer. But 

 the only clay which is known to be newer than the " Purple," 

 is the Hessle clay of Messrs. Wood and Eome, 1 and between 

 it, and the bed under consideration, there are no points of resem- 

 blance. The number and size of its sharp-angled blocks ; the 

 rarity of chalk fragments ; and the distance which most of the 

 boulders must have been carried, make it impossible that this could 

 have been the product of the coast-ice of a limited submergence, 

 which derived its blocks from a pre-existing clay. It is difficult to 

 conceive how anything short of a general Ice-covering could bring 

 distant Carboniferous blocks of such size, and in such abundance. 

 It more nearly resembles the description which Mr. S. V. Wood gives 

 of the upper part of the Purple clay 2 north of Flambro', to which 

 he has given the name of " Purple clay without chalk," and in 

 which he believes the Shap blocks to occur, — bespeaking a wide 

 expanse of ice. 



1 Quart. Journ. Geol. Soc. 1868, vol. xxiv. p. 146. ■ Q. J. G. S. vol. xxvi. p. 90. 



