TERTIARY SHELL MARL. 435 



This formation, has been found in Vermont, in western New 

 York, and probably exists in many parts of all the other northern 

 states. I have never heard of its existence in Virginia, but infer 

 that it is to be found in the western and mountainous region. It 

 may be sought for with the greatest probability of success, in 

 regions where ancient lakes or pools had been filled by gradual de- 

 positions and especially if such waters had been impregnated by 

 carbonate of lime, affording abundant supply of material for the 

 shells of the animals. A cool and moist mountain region also 

 favours the formation of peat. The presence of this substance is 

 connected with that of such shelly deposits below only so far as 

 this : that the collections of waters which would produce and 

 finally be filled up by the gradual deposition of shells, in such a 

 climate, would be most apt to invite the formation of peat subse- 

 quently. Therefore, under peat, if in hollows, the deposits of such 

 shell marl are most likely to be found. 



B. Tertiary fossil sea-shell Marl. 



The second division of shell marl is the great and almost only 

 marl of the tide-water region of Virginia and also of Maryland, 

 the Carolinas, and Georgia. It was produced by the gradual depo- 

 sition and accumulation of the shells left by the animals, mostly of 

 species now extinct, which had lived and died in them, on the bot- 

 tom of the ancient ocean. This former bottom of .the ocean was 

 subsequently elevated, by some great convulsion of the earth, much 

 above the original level, and generally much higher than the sur- 

 face of the ocean waters. Thus, these wide-spread beds of shells, 

 with the various admixtures of sand, clay, or pulverized shells, 

 brought by currents, or the force of the waves, became high land; 

 and the different conditions and qualities are such as might be in- 

 ferred from the different operations of the original producing 

 causes, with the additional, aid of a subsequent state of rest for 

 countless ages. After the production and accumulation of these 

 beds of shells, to depths varying with circumstances, a mighty 

 flood, proceeding from the direction of the present higher lands, 

 swept over this great region, washing off and carrying away much 

 of the higher parts of these shelly beds, and then covering the re- 

 mainder with the drift of various earths brought and deposited by 

 this great land flood. Thus the beds of fossil sea-shells are gene- 

 rally thin in lower Virginia, and entirely wanting in many and 

 wide intervals ; and are mostly covered by a far greater thickness 



ter snail (helix putris, Linnseus), others are bivalves (generally tellina, ani- 

 mal tethys, Lin.) From this deposit, the proprietor had sold as much for 

 manure as brought him 12,000 sterling, in the twelve years after its use 

 had been begun. 



