Yol. 62.] THE CLAY-WITH-F LINTS. 141 



of Ciay-with-Flints, and I felt equally sure that different kinds of 

 clay differ also in weight. 



In Sir C. W. Pasley's book on 'Limes & Cements' x it is stated that 

 ' one cubic foot of solid chalk, such as is obtained near Chatham, 

 weighs when perfectly dry about 90 lbs.' ; but in a table on p. 142 he 

 gives the weight of a cubic foot of pure dry chalk as 94*99 lbs., which 

 is practically 95 lbs. The chalk to which Pasley refers was probably 

 obtained from the zone of Micraster cor-testudinarium. Desiring, 

 however, to have confirmation or correction of this, I asked Mr. W. 

 Hill to ascertain the actual weight of small cubes cut from the 

 samples of chalk sent to him. This he did, dissolving the cubes 

 afterwards, with the results already recorded. Pieces were cut and 

 trimmed as accurately as possible to form 1-inch cubes ; they were 

 dried for 5 or 6 hours at 120° C, and then weighed, with the 

 following results : — 



Grammes. 

 Cube of Keinenham chalk weighs 26*05 



„ Knebworth „ ,7 25"28 



„ Culhani „ „ 32*19 



„ Winnal „ „ 30-25 



4) 11377 = average 2841. 



These results show that there is considerable variation in the 

 weight of pure white Upper Chalk, even in the same zone of 

 Micraster cor-anguinum, to which the last three belong. Let us 

 first consider the Eemenham chalk, for Sir C. W. Pasley's Chatham 

 chalk probably came from the same zone. The weight of one 

 gramme is *002 of a pound, consequently 1 cubic inch of Remen- 

 ham chalk weighs *0521 of a pound. Multiplying this by 1728, we 

 find that a cubic foot of the same chalk will weigh slightly over 

 90 lbs., which is the weight given for Chatham chalk — a curious 

 coincidence. 



The mean weight of all four samples is 28*44, and this, multiplied 

 by *002, gives -05688 of a pound ; and again, multiplying by 1728, 

 we get the result that a cubic foot of the average kind to be found 

 in these two zones weighs 98*288 lbs. This is rather more than the 

 greater weight given by Pasley, but we shall not be far wrong if we 

 take the weight of a cubic foot of such chalk as 98 lbs. 



The determination of the weight of a cubic inch of Clay-with- 

 Plints proved to be much more difficult. The plan adopted was to 

 square roughly with a knife and then dry the cube, finally to dress 

 it accurately with a file, and test it with calipers. Some samples, 

 collected in dry weather, broke up so much that only half-inch cubes 

 were obtainable; others, although moist, were sandy and friable for 

 that reason. Out of many samples tried, Mr. Hill has only been 

 able to make five satisfactory cubes, and three of these were half-inch 

 cubes. Prom a sample obtained from the top of a quarry at Kneb- 

 worth he cut two half-inch cubes, the mean weight of which was 



1 2nd ed. (1847) pt. i, p. 4, 8vo. London. 

 Q. J. G. S. No. 246. m 



