CALCAREOUS MANURES— APPENDIX. 205 



And in a subsequent digging the strength of four specimens of the blue part 

 of the marl was as follows : 



In the first foot depth of blue nnder-stratum - - 32 per cent. 



In the second foot - - - - - 33 " 



At 3| feet ...... 76 " 



At 4 leet, and lowest digging then effected - - 70 " 



It may readily be inferred, from these various results, that if one or two 

 specimens only had been analyzed, and these taken with no more care than 

 is commonly used, that a very deceptions report might have been furnished 

 from making even the most accurate analyses. 



r onchologlsts and geologists, who have treated so much of marls but 

 merely in reference to the shells they furnish, or to their geological character, 

 speak of the blue marl as formed by shells being imbedded in a blue clay. 

 But the earth is not generally a clay, nor any thing even approaching to a 

 clay, but is mostly of silicious sand. The ordinary blue marl contains 

 usually from three to four times as much pure silicious sand as of clay. 

 From various specimens of two diggings in such marl, from which more 

 than 300 acres were marled of tlie C'oggins' Point farm, the following 

 results were found by analysis : 



Yellow marl (wet) thin layer at top, contained of carbonate of lime 24 grains. 

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

 form dull blue color, 100 grains contained: 



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



White silicious sand, 47 



Clay, black when moist, and dark gray v.'hen dried, - - 19 



100 

 Like 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 con- 

 tained of carbonate of lime - - - - - - 29 



At 6 feet deep, (the shell not much reduced,) carbonate of lime 44 

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



Some few hard lumps of conglomerated shells and earths 

 scattered through the general mass, 73 



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

 pearance and believed to be the same body as the preceding, the general 

 average of strength, as obtained fiom several trials at different depths, was 

 in 100 grains of marl, 35 of caroonate of lime. The thicloiess of this 

 body, where penetrated, varied from 11 to 14 feet; where there was a 

 marked though not entire absence 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 tlie vaiious 

 diggings made by myself, or of others heard of, has the bottom of the marl 

 been reached— though in many, and must generally when penetrated deeply 

 enough, it becomes so poor as to be not worth the labor of removing. 

 In the only 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 in Prince George 

 county, my then residence, after passing through a bed of firm blue marl, 



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