140 me* a. j. jukes-browne on [May 1906, 



(2) Residues in the Zone op Micraster cor-axguinum. 



Grammes. 



Chalk from Blandford (Dorset) 119 



Durnford (Wilts) 2-00 



Winnal (Hants) 081 



Orondall (Hants) 1*46 



Culham (Berks) 1-38 



Knebworth (Herts) 215 



Dover (Kent) T20 



7)10-19 = average of 1'45. 



(3) Residues in the Zone of Marsufites. 



Grammes. 



Chalk from Blandford (Dorset) 1*10 



,, ,, Arundel (Sussex) 1*24 



„ Margate (Kent) 0"99 



„ Salisbury (Wilts) 095 



., Crondall (Hants) 0*87 



5)5-15 = average of 103. 



(4) Residues in the Zone oe Aciikocamax quadratus. 



Grammes. 



Chalk from Whaddon (Wilts) 0-687 



„ Milford (Wilts) 0"607 



„ Culver (Isle of Wight) 0753 



„ Otterbourne (Hants) l 0*880 



4 )2-927 = average of 073. 



Prom the foregoing analyses it appears that there is a gradual 

 diminution, in the amount of insoluble residue as we ascend in the 

 Upper Chalk, from the zone of Micraster cor-testudinarium to that 

 of Actinocamax quadratus. If we take the two lower zones together, 

 as constituting that part of the Chalk in which flints are most 

 numerous, we find that equal quantities of them will yield an 

 average percentage of 1*54 of insoluble residue. The solution of 

 equal quantities of the two middle zones will yield 1*24 per cent., 

 and equal quantities of the two higher zones will yield only 0*88 

 per cent, of insoluble residue. 



This, however, is percentage by weight ; and if we wish to 

 calculate how many cubic inches of residue will be left by the 

 solution of a given mass of chalk, we must allow for the difference 

 in the weights of chalk and clay. Here, again, it has been necessary 

 to make special experiments and estimations for the purpose of this 

 paper, because the required information did not exist. Thus I 

 could not find that anyone had determined the comparative weights 

 of different kinds of chalk, I could find no record of the weight 



1 This is taken from an analysis made by M. Duvillier, and published by 

 Prof. Barrois in his ' Recherches sur le Terrain cretace superieur de l'Angle- 

 terre & de l'lrlande ' 1876, p. 42. 



