Marls. 97 Sxpofure to the aip> and moiflure; On CementSi 121. It has, however, been obferved by Mr. Ma- quer, that limeftones, which contain only 0,15 or 0,16 of argill, poffefs all the properties of limeftones; Mem. Par. 1728 : yet this muft be reftrained to the cafe in which they are not ex- pofed to an high degree of heat, or he muft mean pure argill; fcr, if they contained that proportion of clay, they woüld undoubtcdly be fufible. This family, like the foregoing, is divifible into two branches; the one, in which the argii- laceous partof the clayexceeds the filiceous; the other, in which the filiceous is to the argillaceous in a higher proportion than 4 to 1. ift Branch. Of this fort, I do not recolledt that any have as yet been analyfed. 2d Branch* Silictfemis Marls. Tbefe, as beforc faid, poflcfs the fame charae- ters as the foregoing, except that they do not harden when calcined ; nor does the refidmim, after folution in acids, form a brick. Thefe properties, it muft be underftood, arc fufceptible ot various gradations, as the compofitions necef- farily vary from each other. Of this fort, a few ^ are