Petrographic Group 3: Group 3 represents clay typical of calcareous soils such as rendzina and grumusols. The matrix is calcareous, optically active and silty, and rather porous. The non-plastic inclusions are predominanatly calcareous. They include rounded microfossils, chalk, limestone and calcareous concentrations. The most common are the microfossils and chalk in fine to coarse sand size, which together usually accounts for 20-40% of the slide area Quartz also accounts for 5-20%.