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Of the Calcarectis Genus. 373 Moulds are loams mixed with animal and vegetable remains, particularly from putrefaftion; generally ofa black, brown, yellowifti, or greyifli brown colour; the proportion of thefe is highly intereftin<* to agriculture; it can be prettv nearly determined by comparing their weighe when dried at i40°of Fahr, with that which they lofe by be- ing heated to rednefs in an open fire, continued as Ion 0- as any coaly fubftance remains in them ; yet not'exadflv, without fome nicer operations, as the animal earthswill ftill remain undetermined, and alfo the vegetable afhes. -.1. ^ - • Of the Calcareous Genus. Umefionts are frequently intimately mixed > not only with filiceous particles, and calces f jron, as we have already feen ; but alfo with ar- crillite in various marbles, fee Lejke G. 328. Vv’hen mixed with filiceous particles in confidera- ble proportion, they effervefee with acids, but llightly, and flow ly, and their fradture tends to the conchoidal, but often alfo to theearthy; of this we have a remarkable inftance in Leike S. 229. Its luftre, o. Hardnefs, fcarcely Frag ments, 3 ; which indicates the filiceous ingredi- ent. Its fp. gr. only 2,254, which fliews it to be ofthenature of fandftone. Heated to 141'’, it did not form a lime, nor did it melt. When the limeftone is of the granulär kind it has more luftre and is much heavier, fee l.efke 8. 1098. But when the particles of filex are in a fmaller proportion, or not purely filiceous, the limeftone preients a diff rent appearance; thus the lime ftone, Leike 8. .7Ö9, feem« a« if paffing mto hornftone, and is of a yellowilh &rey colour. Lulrre, 0. l'ranfparcncy, 1. Fiacture ftne q>linttry. B b 3 Fragments,