The compact basalt alternates with the strata of porous basalt and marl.

The bed of the lake also consisted of a very white marl.

The red marl must almost certainly have been black slate somewhere, somewhen.

Thus, Puvis recommends marl, while the Roret Manual is opposed to it.

Of calcareous soils we have three varieties, viz.-limestone ,limestonegravel, and marl.