37 



phate of iron (or copperas,) sulphate of alumina (or alum,) and 

 sulphur in an uncombined condition. So large a proportion of 

 these substances is sometimes present, as to render the water* ob- 

 tained from the strata in which they exist, absolutely unfit for 

 use. 



It is to the existence of these materials in the strata, that we 

 are to look for the cause of the disappearance of the calcareous 

 matter, in the form of shells, which they once evidently contained. 

 Either of the sulphates above named would exert a rapid decom- 

 posing action on the carbonate of lime, of which shells principally 

 consist. The sulphuric acid of the sulphate combining with the 

 lime of the carbonate, thus converting it into gypsum, while the 

 carbonic acid would, in great part, escape in the form of gas. That 

 the gypsum is not now discovered in these beds, is an obvious result 

 of the comparative solubility of that substance in water; its conti- 

 nuance in the strata being only possible where a heavy covering of 

 clay excluded the percolating liquid. 



Useless, if not injurious, as these clays are now believed to be 

 when applied to land, there is reason to think that they are capable, 

 by a little application of chemical knowledge, of being rendered 

 truly valuable as an auxiliary manure. The gypsum into which 

 their enclosed shells were once converted, would doubtless have im- 

 parted to them a high agricultural value. Can we not replace, if not 

 all, some portion of this fertilizing material, by mingling the clay with 

 the more pulverulent shell marls occasionally found in its vicinity? 

 That this mixture would result in the conversion of a portion of 

 the shelly matter into gypsum, there can be no doubt ; and where 

 the clay was originally rich in copperas and alum, the amount of the 

 gypsum thus compounded would be proportionally great. Experi- 

 ments on this subject are well worthy of being tried, not only with the 

 clays here mentioned, but with those of a similar nature, which, as 

 already remarked, occur in the more eastern portion of the Tertiary 

 districts of the state. 



Before the amount of gypsum to be anticipated from such a treat- 

 ment of these materials can be estimated, a chemical determination 

 of the proportion of sulphates of iron and alumina must be had, and 

 to this point future analysis might be usefully directed. 



But though much of the Miocene marl in this district has been 

 exposed to the destructive chemical agencies above explained, much 



