430 FORMATION OP TRUE MARL, 



This marl was thus found in two of my diggings, one on Cogging 

 Point farm, and the other at Shellbanks, in Prince George county. 

 In both cases, though perfectly characterized, the quantity of true 

 marl was too small to be used separately from the more calcareous 

 and much thicker stratum of shell marl below. This true marl was 

 in many horizontal layers, few of which were severally more than an 

 inch in thickness, separated by other layers, sometimes very thin, 

 of almost pure shells, broken very small, with some only of the 

 very smallest entire. The pure argillaceous marl is blue (though 

 sometimes of bun 7 colour), firm and compact, breaks easily, but does 

 not bend however moist, and is cut smooth by a knife, leaving a 

 surface like that of hard soap. This marl contained, in the argilla- 

 ceous part, free from the shelly parts, only 10 per cent, of calca- 

 reous matter. Several other specimens, from other localities in the 

 same region, were about the same strength. Therefore, even if 

 more plenty, there would seem to be no inducement to use our true 

 marl where the beds of fossil shells, called marl, and usually so 

 much richer in calcareous matter, can be drawn from. But in Eu- 

 rope, clay marl is reported as rich as 40 to 60 per cent, of calca- 

 reous matter, and indeed richer, gradually running into lime-stone 

 or impure chalk.* 



But though it is proper to know, and to bear in mind, what is 

 understood by the term marl, by mineralogists, and by the best in- 

 formed English and French agricultural writers, in regard to the 

 extensive rnarlings in those countries, yet it is necessary in Virgi- 

 nia to conform generally to the usage which gives the name of marl 

 to all earths largely mixed with fossil shells, or their fragments ] 

 and as the term is so far improperly extended, I would carry it still 

 farther, and make it embrace all natural calcareous earths not of 

 stony hardness. This arrangement then would indeed include true 

 marl, but merely as one class, and that one the least noticeable for 

 abundance or value of all in this country. The following scheme 

 of classification will conform to this view, and serve to make more 

 clear the descriptions that will follow : 



*Such cases as are named above can scarcely be deemed exceptions to 

 the entire non-existence of true marl in this region. These limited de- 

 posits were doubtless formed by the abrading, stirring up, and suspension 

 of the upper part of the beds of shelly earth, by some strong current or 

 agitation of the sea, and the subsequent deposition of the finest parts in 

 tranquil water. The small shells and shelly powder sometimes seen be- 

 tween these layers of clay marl, were brought and deposited during other 

 intervals of more agitated water. I have often seen such deposits of per- 

 fect true marl, artificially produced, in the small open drains of marl-pits 

 (of our fossil shells), by the gradual settling of the suspended fine earthy 

 matters from the turbid water. 



