248 Binocochlea ing ens from the Wealden Beds, Hastings 



In the sandstone within an inch or two of the blue core there was 

 found only 0-73 per cent CaO corresponding to 1-30 per cent CaCOg, 

 so that this part of the concretion is almost free from calcite cement. 



To test the question of whether any change in bulk accompanied 

 the change of bluestone to sandstone the volume of a weighed mass 

 of the dry sandstone was determined by coating the sandstone 

 with a thin waterproofing coat of varnish, and determining its 

 effective density in that condition. Two determinations gave a 

 value for this effective density of 1-9. This approximates very closely 

 to the value one would expect if the whole of the calcite of the blue- 

 stone were removed without any change in the volume occupied by 

 the resultant sandstone as is shown by the following calculation :— 



The density of the bluestone containing 32 per cent of CaCOg 

 was determined as 2-62. One hundred grams of bluestone will, 



therefore, occupy a volume of = 38-16 c.c. 



^^ 2-62 



The removal of the whole of the 32 per cent CaCOg will reduce the 



weight of the rock from 100 to 68 grams. 



If this removal is unaccompanied by anv change in volume, it 



68 

 will have an efiective density of r— —, = 1-8. The value found for the 



•' 38-16 



sandstone is 1-9. 



Admittedly this is only a very approximate calculation, but the 



agreement seems close enough to show that a bluestone of the type 



forming the inner part of the concretions can lose the whole of its 



30 per cent of calcite and give rise to the sandstone of the outer 



shells without any suffering change in volume and therefore without 



the disturbance of the outer form of the concretion, or the destruction 



of any structures within it. 



EXPLANATION OF PLATES X AND XL 



Plate X. 



Pliotograph taken by Mr. H. T. Pottinger of the greater part of the prmcipal 



dextral specimen as it lay where found. The remains of the shattered apex 



were scattered towards the right ; the body -whorl to the left did not come into 



the picture. 



Plate XL 

 A. — Sinistral form : — 



FIG. 



1, 2, 3. — Associated fragments of one individual, representing whorls 1-7, 



10-12, and 13-15. 

 4. — Portion of another individual representing whorls 12-16 (?). 

 5. — Portion of three whorls (13-15 ?) of a third individual. 

 6. — Apical view of the nucleus of the dextral specimen ( = Fig. 1 of B). 

 B. — Dextral form : — 



FIG. 



7-6. — Associated parts of the individual shown in PI. X, and representing whorls 



1-2, 4, 7-9, 11-14, 15-21, and 22-23 respectively. 

 7, 8. — Portions of other individuals with flatter whorls, showing the twofold 



fracturing resulting in the formation of wedge-shaped pieces. 

 9. — Portion of another example with more tumid whorls. 

 10. — Apical view of the nucleus of tlie sinistral specimen ( = Fig. 1 of ^). 



