18 DESCRIPTION OF THE STRATA. 



As the brown clay passes into the ash-coloured, so the latter 

 passes into the blue clay, which often occurs in patches, rather than 

 in a distinct bed. Indeed, all the three kinds of clay ai'e often seen 

 blended together in one mass : but we generally find the brown clay 

 uppermost, the ash-coloured in the middle, and the blue tenacious 

 clay in the lowest place. 



These beds, or divisions, of the alluyial covering, are pei'haps as - 

 regular as some of the beds of clay and gravel lying over the chalk iii 

 the south of England, which are regarded by many as part of the 

 regular strata : but since all the beds now enumerated contain more 

 or less of the fragments of rocks of almost all descriptions, and since 

 we find nearly the same succession of beds over the sandstone near 

 Whitby, as ax'e over the chalk in Holderness, it seems most proper 

 to consider the whole as an alluvial covering. Perhaps it may be 

 fairly questioned, whether the beds of sand and gravel at Woolwich 

 and other parts in the south, which have been described as properly 

 stratified, be any thing more than a part of the alluvium ; and the 

 same remark may very possibly apply to those gravel beds in France 

 and elsewhere, which have been dignified with the title oi fresh-ivater . 

 formations. 



At the same time, if any shall affirm, that the sand beds in what 

 Ave have described as alluvium, might in other circumstances have 

 become sandstone, that the marl might have formed limestone, and 

 the clay have become shale, we will not dispute the matter wdth them. 

 In fact, there are spots where we find marl so indurated as to ap- 

 proach very near the state of limestone; the clays, particularly the 

 darker coloured clays, almost in the state of shale ; and the beds of 

 sand and gravel actually hardened into solid rock. An instance of 

 this last kind may be seen between Whitby and the Lector Nab, 

 where some springs that issu^e from the middle of the cliff, and 

 deposit lime and oxide of iron, have not only formed calcareous 



