246 Professor Hailstone on the 



The appearance of these specimens is not very inviting ; but 

 they are not without interest. 



The pebbles of hard chalk are probably the remnants of the bed 

 which immediately covers the green sand and the gault^ of which 

 these are either fragments rounded by attrition, or they are the 

 nodules peculiar to the lower chalk, (as may be seen in Wiltshire,) 

 washed out of the bed itself, which is disintegrated. 



No. 2 Improbably a variety of common flint; specimens of this 

 substance are not uncommon, in which there is an appearance^ as 

 in a Scotch pebble, of alternate layers of deposition. The action 

 of air and moisture might render these natural divisions more 

 visible, just as slates are obtained by the exposure of the blocks of 

 fissile stone to the weather. 



As other beds, besides the London clay, contain septaria, we 

 cannot say from what bed the fragments of this substance are 

 derived j nor will any of the specimens previous to No. 6, furnish 

 any data for guessing the nature and direction of the current, 

 which has heaped together this mass of confusion. 



The mass of greenstone nearest to Cambridge is found in the 

 loadstone beds of Derbyshire, to some specimens of which the 

 pebble No. 6, bears a close resemblance. Few of these pebbles 

 vv^eigh less than 8 ounces. 



The large oyster is the same with fig. 7 and 8 of PI. 8 of 

 Townshend's work, and belongs to the bed which underlies the 

 coral rag. 



The large belemnite is peculiar, I believe, to the lower oolite. 



The bassetings of the three last mentioned beds, that is, of the 

 toadstone, the coral rag and the lower oolite, are found (at least in 

 England) only in a direction west of Cambridge ; so that we are 

 led to explain the accumulation of these alluvia by the agency of a 

 powerful current flowing from, west to east. 



