20 THIRD SUPPLEMENT TO THE CRAG MOLLUSCA. 



I take this opportunity of correcting the representations given by Mr. Harmer and 

 myself of the beds of the Crag district in the map, and sections which accompany the 

 " Introduction " to the first Supplement to the Crag Mollusca in the volume of the 

 Society for 1871, so far as subsequent observations have rendered necessary, as follows: 



Owing to the obscurity existing where sand rests on sand, the Lower Glacial sand, 

 No. 6 of the map, is not shown further south than the neighbourhood of Dunwich ; and 

 in the section (A) through the Red Crag area it is omitted altogether, and the Middle 

 Glacial (No. 8) represented as resting throughout on the Red Crag. Residence in the 

 district since 1873 has afforded me the means of a closer examination and comparison of 

 pit sections there, and convinced me that this representation (which was mine only) was 

 erroneous, and that the sand No. 6 is not only present, but is the principal formation in 

 this area ; for though it is mostly underlain by Red Crag, it in many places takes the 

 place of this, and rests direct on the London Clay. Over the Red Crag, however, there is 

 in some excavations a reddish-brown sand, soft, loamy, and destitute of the smallest 

 fragment of shell, but in which sometimes masses of shelly crag are enveloped, and in 

 which, in some rare instances, bands of ironstone containing casts of Red Crag shells also 

 occur. This sand is merely the Red Crag from, which the calcareous constituents have 

 been carried away by dissolution in water, while the argillaceous and ferruginous consti- 

 tuents have been either left unaffected, or else redeposited in the undisturbed sandy mass. 

 The difficulty, therefore, is to distinguish between this and the sand No. 6 ; for in South 

 Suffolk the latter loses the shingly or pebbly character which enables it to be easily 

 recognised in North East Suffolk and in Norfolk. Over the Red Crag area the sand 

 No. 6 passes upwards by the mere substitution of argillaceous for arenaceous sediment 

 into stratified brickearth, just as it does on the Cromer Coast and generally in North 

 Norfolk, though from its geographical position in South Suffolk this brickearth has not 

 there received that copious intermixture of chalk debris and chalk silt which along the 

 Cromer Coast (where it is represented by the " Contorted Drift," bed No. 7 of the Map, 

 &c.) forms its preponderating constituent, in proportion to the diminution in its distance 

 from the Lincolnshire Chalkwold, from the degradation of which by the land ice 

 during the earlier part of the Glacial period, when England was undergoing its great 

 submergence, this debris and silt were derived; but thin layers of this debris are 

 sometimes present in it in South Suffolk, as e.g. at Kesgrave. Neither has it been so 

 disturbed by the action of grounding bergs as in North Norfolk, where the result of this 

 action has obtained for it the name of " Contorted Drift ; " nevertheless, it is sometimes 

 contorted in Suffolk, as I observed in an excavation of it beneath the chalky clay on the 

 Hasketon side of Woodbridge in 1874. Over the Red Crag area this bed has suffered 

 'so generally and extensively from the wash of the sea during the emergence of the 

 country, when the Middle Glacial gravel (No. 8) was in course of accumulation, and 

 the lan.d ice, of which the chalky clay was the moraine, was extending from the Wold to 

 follow the retiring sea, that only patches of it remain there. One of these patches, that 



