Observations of the panoramic photographs transmitted by Veneras 13 and 14 indicate that many visible rock units are layered and that at least a portion of the fine material could be the result of in situ geomorphic disintegration. Chemical and material property experiments indicate that the chemical composition of the material at the landing sites is essentially basaltic, that the bearing strength is minimal (a few kilograms per square centimetre, or a few hundred kilopascals), that the density is less than 1.5 g/cm3, that the porosity is very high (>50%), and that the electrical resistivity is very low (<90 ohm · m).
The discussion on the possible geological nature of the surface of Venus presented in Part I (Florensky and others, 1977a) is extended in light of these new data. Six possible origins of the rock units were discussed: (1) surface lava extrusion; (2) igneous intrusion, later exposed by erosion; (3) pyroclastic fall; (4) impact ejection and lithification; (5) sedimentary deposits lithified at depth and later exposed by erosion; and (6) surface metamorphism due to unique Venusian surface conditions. It is concluded that, although none of the above hypotheses can be conclusively proven or disproven, hypothesis 6 is to be advanced to the forefront. This is suggested by (1) the low density and low bearing strength, (2) the presence of layering, (3) the possible presence of sedimentary structures in the rock units, such as cross-bedding and ripple marks, (4) the low electrical resistivity, which may indicate chemical alterations of surface material, and (5) the albedo of the loose, fine material, which is lower than the albedo of the rock units. This again suggests chemical alterations.
Within the context of this hypothesis, the rock units are sedimentary or sedimentary-volcanic. Lithification occurred in the past due to surface chemical effects. The rock units, analogous with a similar terrestrial phenomenon, can be referred to as “duricrusts” (with the understanding that the Venusian process is completely different from the terrestrial process). Presently, the rock units are undergoing disintegration, indicating that changes have occurred in the surface conditions at the landing sites.