MO ALLUVIAL ROCKS. with honey-Jlone. Naturalfulphur,Jlaggy mineral-' pitch, and cryftals of felenite, fometimes alfo oc cur in it. Bog iron-ore—is a very important alluvial rock. It occurs frequently in moorilh places. It may be confidered as partly a mechanical, and partly a. chemical depofite. Nagelfluh.—This rock is ufually compofed of fragments of limeftone, more or lefs rounded, and of various magnitudes, cemented together by a bafis of calc-finter. It occurs always at a greater or lefs diftance from limeftone mountains, and fometimes forms confiderable tra&s of country. It appears abundantly at the foot of the great hills of alpine limeftone, that bound Bavaria to the fouth, and in many other places of the great lime ftone range that paffes through the Tyrol, Styria, &.c. 2. Chemical alluvial depo/itions. — Thefe are calc-tuff and calc-finter, which are the neweft members, if we except coral, of the great lime ftone formation-fuite. (i.) Calc-tuff.—It occurs in beds, and thefe have different degrees of denfity; fome being earthy, and others porous. It occurs ufually in the vici nity of limeftone mountains, and in deep places. It often includes gramineous plants, mofTes, and leaves of trees, which are more or lefs altered. But the moft remarkable circumftance, is its con taining