S06 GEOGNOSTICAL SKETCH, &C. 
observed red sandstone and its conglomerate, occasional 
pieces of white sandstone, but never any of the secondary 
porphyries or trap-rocks. Clay occurs but seldom, and 
hence the sandy nature of the soil in this district, and con- 
sequent badness of the crops in dry seasons. Marl has been 
discovered in one or two places, which were formerly the 
bottoms of fresh-water lakes, but which are now deeply in- 
crusted with a layer of peat* 
