94 Calcareous Genus. Marls, or Calcareous Marls ift Family. In an earthy or femi-indurated form. Mergel erde of Werner. Generally yellowifh grey, more rarely yellow- ilh white. Luftre o. Tranfparency o. Surface dufty. Slightly compadfed together, frequently loofe. Feels dry and rough. Spec. grav. from i,6oo to 2,4. It ftrongly efFervefces with acids, and, when difi'olved therein, the refiduum, dried in a heat of ioo° Fahr, weighs from 4 to 4. of thewhole; that is to fay, this marl contains from 30 to 80 per ct. of calx. It is fufible in a heat -of from 130° to 140° of Wedgwood. In water it foon falls into powder, and is not dudtile; the compadted part farther moulders by expofure to the air. It confifts of mild calcareous earth, in the pro- portion of from 66 to 80 per ct. the remainder clay, with which mica, and other foreign ingrc- dients, and frequently fhelis, are mixed. i3ut clay itfelf contains two ingredients, namely, argill and filcx; and hence this family divides into two * Though there are different diflindfions of marls, yct by the terin marl, «ithout faither addition, calcareous mail* are undtrllood. branches;