94 PEOF. J. PEESIWICn ON THE EELATION OE TFE 



It thus appears that of the 18 species from the Southwold sections 

 13 are recorded in the Biire Valley; whilst of the other species, 

 three {Melamjpus pyramidalis^ Cerithium tricinctum, and Paludina 

 media), which are characteristic of the Pluvio-marine Crag, have 

 not been met with in the Bure-Valley Crag. The other two are 

 also Norwich species, but have a wider range. On the other hand, 

 of the 36 species quoted from the Bure Valley, 16 are wanting at 

 Southwold, amongst which is the only characteristic shell of that 

 Crag, Tellina balthica, while other such common Westleton and 

 Bure- Valley shells as Scalariac/rceytJandica, NdticaJielicoides, Astarie 

 compressa, Ltda oblongoides, and Mytilus edalis are also wanting. 



§ 3. Choice of Terms. 



The main objection, however, to the adoption of the " Bure- 

 Valley Crag or Pebble-beds" as terms for these geological zones, is 

 that neither their palseontological value nor their stratigraphical 

 relations are in that district free from uncertainty. Where the 

 Chillesford Clay intervenes, there is no doubt of their distinctness ; 

 but where this bed is wanting, as is commonly the case in Norfolk, 

 it is almost impossible to distinguish between the beds above and 

 the beds beneath that zone ; and as, in consequence of the Pebbly 

 Beds resting upon an eroded surface of the Chillesford Beds, the 

 juxtaposition of the two shell-beds is of frequent occurrence*, their 

 duality then is lost. At Norwich this distinction still exists ; but 

 further northward, in the Bure Valley, the Chillesford Clay is 

 either wanting or else exists in a very fragmentary form ; so that, 

 in such cases, owing to their having many characters in common, 

 the distinction between the Pure-Valley and Norwich-Crag beds 

 might pass unnoticed. 



It may, in fact, be a question whether the thin seam of clay 

 which in Mr. Wood's typical sections of Belaugh and Wroxham is 

 intercalated near their base (see Mr. Woodward's memoir, pp. 60 

 and 62) does not represent the Chillesford Clay, and whether in the 

 sfime way the thin occasional bed of clay a foot or two above the 

 Chalk in the coast-section is not also of the same age, and whether 

 the lower shell-bed in these several localities should not be referred 

 to the Norwich Crag instead of grouping it with the overlying beds 

 under the term of the " Weybourn Crag," or as the " Lower Glacial '' 

 of Mr. Wood. (See Supplement to the Crag Mollusca, pp. 203 -219.) 

 To test the point, I would keep the fossils from these beds separate 

 until their exact relationship is ascertained with greater certainty. 

 Mr. Woodward's short lists, at pp. 62 and 63 of his Norwich memoir, 

 show slight but not unnoticeable differences between the upper and 

 lower part of the section. Tellina baltJdca, which is stated by 

 Messrs. Wood and Harmer to be almost the only shell in the Pebbly 

 Sands that does not occur in the Norwich Crag, is not found in the 

 lower bed at Wroxham, although it is at Belaugh ; but I tliink (for 

 reasons to be given hereafter) with Mr. Woodward, that the occur- 



* Quart. Journ. Geol. Soc. vol. xxvii. p. 456 (1871). 



