calc-tufa

These are chambers excavated in the tufa on either side of the galleries, with which they communicate by doors, as seen in Fig. 4.

For the same reason the different piani were generally separated by a thick stratum of solid tufa.

At B will be observed the employment of masonry to strengthen the crumbling walls of the friable tufa.

The tufa granolare, on the contrary, was admirably adapted for the construction of these subterranean cemeteries.

The most ancient and lowest stratum of this igneous formation is a compact conglomerate known as tufa lithoide.