BLUE MARL. 447 



Within 24 inches of top, shelly matter finely divided, and the 

 mass uniform dull blue colour, 100 grains contained : 



Carbonate of lime, 34 grains. 



White silicious sand, . . . . 47 " 



Clay, black when moist, and dark gray when dried, 19 " 



100 



Of similar blue marl from another pit in the same body, 100 

 grains contained : 

 Carbonate of lime, ...... 34 grains. 



Silicious sand, ...... 52 " 



Clay, 14 



100 

 Of another specimen from the same, and of similar 



marl, 100 grains contained of carbonate of lime, 29 t( 



At 6 feet deep (the shell not much reduced), carbo- 

 nate of lime ....... 44 <e 



At 13 feet deep, and one foot from bottom, . 33 " 



Some few hard lumps of conglomerated shells and 



earth scattered through the general mass, . 73 " 



From a digging at three-fourths of a mile distant, of marl of the 

 same appearance and believed to be the same body as the preceding, 

 the general average of strength, as obtained from several trials at 

 different depths, was in 100 grains of marl, 35 of carbonate of lime. 

 The thickness of this body, where penetrated, varied from 11 to 14 

 feet ; where there was a marked lessening, though not entire ab- 

 sence of shelly matter, and increase of silicious sand of the same 

 blue tint. The deeper removal was stopped because of the obvious 

 poverty, and no further examination of more than a foot or two in 

 depth was made in this poor substratum. In but few of all the 

 various diggings made by myself, or of others heard of, has the bot- 

 tom of the marl been reached though in many, and most generally 

 when penetrated deeply enough, it becomes so poor as to be not 

 worth the labour of removing. In most of the few known cases, 

 when digging the marl for manure, that the bottom of the miocene 

 was reached, the stratum below was of eocene green-sand earth, or 

 eocene marl. In digging a well, at Shellbanks, my then residence, 

 after passing through a bed of firm blue marl, of broken (or water- 

 worn) shells, obviously the same kind dug at another place for ma- 

 nure, and described at page 445, a soft brown sand was reached, 

 apparently destitute of calcareous matter, and from which rose an 

 abundant supply of pure and soft water to the height of 13 feet, 

 which stood altogether in this blue marl, without its purity being 

 affected either by the calcareous matter of the marl, or ita colour- 



