RAPID FORMATION OF CHALK. 



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a fact decisive against its being formed by mechanical deposition of 

 drift, or detritus of older limestones. The preservation of the most 

 delicate textures of animals before referred to, proves beyond doubt, 

 that those organic bodies had not been transported from a distance, 

 or subjected to the violent action of inundations or currents. 



The fossil fish found in chalk with the body preserving the nat- 

 ural form, and with the air bladder uncompressed, proves beyond 

 doubt, that the animals were encased in mineral matter, before the 

 putrefactive process had effected the destruction of the fleshy parts. 

 A sudden eruption of thermal water holding calcareous earth in so- 

 lution or suspension, might instantly, deprive the animals of life, and 

 protect their bodies from decay. The matter, called creta by Fer- 

 rara, erupted from Macaluba, was certainly a soft limestone, analo- 

 gous to chalk ; and though the eruption lasted only part of a day, it 

 formed a stratum many feet in thickness. Had this eruption taken 

 place under water, the earthy matter would have been more w^idely 

 diffused, and the stratum of limestone deposited, would have been 

 proportionably thinner. In the case of the fossil fish before stated, 

 we are not obliged to suppose the deposition to be so rapid : several 

 days might elapse, before the body was entirely buried under calca- 

 reous earth. If we say seven days, and estimate the thickness of the 

 fish at three inches, we shall have a chronometer to measure the time 

 required to form a stratum of chalk three inches in depth, which is 

 one week. This is equal to one foot in a month, or twelve feet in a 

 year; and could we suppose the deposition to proceed without in- 

 terruption, it would not require more than ninety years, to form a 

 mass of chalk beds, one thousand feet in thickness; which is more 

 than that of all the chalk beds in England. It is by no means in- 

 tended to support the opinion, that the chalk beds were all deposited 

 in so short a period ; long intervals of repose might pass between 

 different eruptions. My object in calling the attention of geologists 

 to this subject is, to show that strata may be formed more rapidly 

 than they are generally disposed to believe, and that the feeble ope- 

 rations of natural causes in our own times, however similar in kind, 

 bear no proportion, in their intensity, to the mighty agents that have 

 formed the ancient crust of the globe. The deposition of a bed of 

 calcareous earth, a few feet in thickness, in some of the Scottish 

 j lakes, as described by Mr. Lyell, would appear to have required 

 1 many centuries for its completion. In some of the beds of oolite, 

 the quantity of animal remains bears a considerable proportion to the 

 whole mass, and the beds of encrinal limestone in some of our moun- 

 tain limestones, are formed, principally, of the stems and branches 

 of encrinites, probably broken by the violent action of the sea ; but 

 it is not improbable, that the interstices have been filled by calcareous 

 depositions. It is obvious, that limestone strata of considerable 

 thickness, if composed chiefly of organic remains, would require 

 centuries for their completion. 



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