"MAULS" NOT CALCAREOUS. 375 



marl, either as understood by mineralogists and scientific agricul- 

 turists in Europe, or as marl is known in this country. This peculiar 

 formation (the deposit of the shells of fresh-water molluscs in what 

 had been ancienjt lakes, and which since became peat-bogs), has 

 been referred to previously, and will be again, in another connexion. 

 So far, all the earths called marl have been calcareous. But all 

 are not so that are recognised under that name, even by modern 

 and well informed writers, who certainly knew the chemical cha- 

 racter (in this respect), of the earths referred to. In " British 

 Husbandry," a recent work of authority, prepared for and pub- 

 lished by the " Society for the Diffusion of Knowledge," in treating 

 of marl, the following passages occur : 



6. "A bluish marl much used in some parts of Ireland, and long cele- 

 brated as a manure, makes no ebullition with acids ; neither do several of 

 the red marls ; yet many of them are known to be productive of great im- 

 provement to land." p. 265. "Out of 12 specimens of marl submitted to 

 Sir Humphrey Davy, 11 were found to contain calcareous earth; but the 

 result of many other trials of marls, from different parts of the country, 

 and found by farmers to produce an ameliorating effect on the land, yet 

 proves them to be, in many instances, wholly deficient in that substance." 

 See "Marl" in Holland's Report on Cheshire. 



Now whatever of fertilizing properties these earths contained, 

 they were not marl in the proper understanding of that term, nor 

 do they agree with our marl in any stated character, either chemi- 

 cal or physical. 



An earlier, though yet a modern writer, Marshall, has also de- 

 scribed a valuable " marl" of Norfolk, England, which is almost 

 destitute of calcareous matter. 



7. " The red earth which has been set upon the lands of this district, in 

 great abundance, as 'marl,' is much of it in a manner destitute of calca- 

 reous matter ; and, of course, cannot, with propriety, be classed among 

 marls. Nevertheless, a red fossil is^found, in some parts of the district, 

 which contains a proportion of calcareous matter. The marl of Croxall 

 (in part of a stone-like, or slaty contexture, and of a light red colour) is 

 the richest in calcareosity ; one hundred grains of it afford thirty grains of 

 calcareous matter ; and seventy grains of fine, impalpable, red-bark-like 

 powder.* And a marl of Elford (in colour and contexture various, but re- 

 sembling those of the Croxall marl) affords near twenty grains. Yet the 



* This marl is singularly tenacious of its calcareous matter ; dissolving 

 remarkably slowly. One hundred grains, roughly pounded, was twenty- 

 four hours in dissolving ; and another hundred, though pulverized to mere 

 dust, continued to effervesce twelve hours ; notwithstanding it was first 

 saturated with "water, and afterward shaken repeatedly. The Breedon stone, 

 roughly pounded, dissolved in half the time ; notwithstanding its extreme 

 hardness. [I strongly suspect that Marshall used nitric acid in this trial, 

 and was deceived by the slow solution of carbonate of iron, with some 

 ebullition, and that there was as little calcareous earth as in the other 

 cases. I have never experienced such slow solution of carbonate of lime, 

 in strong acid. E. R.J 



