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[177] 



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and variable in magnitude ; some 

 of them scarcely exceeding the 

 size of a bullet, while others are 

 several feet in circumference. Al- 

 though thickly distributed in hori- 

 zontal beds and layers, they are 

 never in contact with each other, 

 but every nodule is completely 

 surrounded by chalk. Flints so 

 commonly enclose the remains of 

 sponges, alcyonia, and other zoo- 

 phytes, that some geologists are of 

 opinion that the nucleus of every 

 nodule was originally an organic 

 body, and Townsend states, ' so far 

 as my observation goes, zoophytes 

 appear universally to have formed 

 the nuclei of nodulated and coated 

 flints. The nodules of flint fre- 

 quently exhibit the internal struc- 

 ture of the enclosed zoophyte most 

 beautifully and delicately preser- 

 ved.'* A theory offered by Profes- 

 sor Buckland is to this effect : "It 

 does not appear possible that flints 

 could have been formed by infil- 

 tration into pre-existing cavities, 

 like the regularly disseminated 

 geodes of the trap rocks. Assuming 

 that the mass which is now sepa- 

 rated into beds of chalk and flint, 

 was, previously to its consolidation, 

 a compound pulpy fluid, and that 

 the organic bodies now enveloped 

 in the strata were lodged in the 

 matter of the rock, before the 

 separation of its calcareous from 

 its siliceous ingredients, the bodies 

 thus dispersed throughout the 

 mass would afford nuclei, to which 

 the flint, in separating from the 

 chalk, would, upon the principle 

 of chemical affinity, have a ten- 

 dency to attach itself. The chalk 

 and flint proceeded through a 

 contemporaneous process of con- 

 solidation; the separation of the 

 siliceous from the calcareous in- 

 gredients being modified by 

 attractions, which drew to certain 

 centres the particles of the siliceous 

 nodules, as they were in the act of 



separation from the original com- 

 pound mass. The distances of the 

 siliceous strata must have been 

 regulated by the intervals of pre- 

 cipitation of the matter from which 

 they are derived ; each new mass, 

 as it was discharged, forming a 

 bed of pulpy fluid at the bottom of 

 their existing ocean, which being 

 more recent than the bed produced 

 by the last preceding precipitate, 

 would rest upon it as a foundation 

 similar in substance to itself, but 

 of which the consolidation was 

 sufficiently advanced to prevent the 

 ingredients of the last deposit, from 

 penetrating or disturbing the pro- 

 ductions of that which preceded it." 

 The present shape of many chalk 

 flints being that of organic bodies, 

 demonstrates the latter to have 

 existed before the consolidation of 

 the former; for the fidelity with 

 which the site has often copied the 

 organization, and even the accidents 

 and irregularities of the bodies 

 enveloped is so accurate, that it is 

 impossible to attribute the form of 

 the flint to any other cause than 

 that of the body on which it was 

 deposited. Sometimes the organi- 

 zation is so delicately retained that 

 it seems not to have undergone the 

 smallest derangement before the 

 siliceous cast was taken, and the 

 model is thus permanently preser- 

 ved. The organic bodies that 

 afforded nuclei to these nascent 

 flints, appear to have been dispersed 

 pretty uniformly through the origi- 

 nal compound mass, which is now 

 divided into beds of chalk and 

 flints, but it is not easy to deter- 

 mine what cause it was that regu- 

 lated the distances at which the 

 beds of flint have been disposed, or 

 to say why we sometimes find 

 organic bodies preserved in flint, 

 at other times enveloped and filled 

 only by pure chalk. In many 

 silicified spunges and alcyonia, the 

 outer crust being composed of flint 



