There cannot be the slightest doubt that, if future explorers will arrange the fossils they obtain from these different strata according to the particular hand from which they are derived, the scanty lists here given will be greatly enlarged.
There is another somewhat remarkable feature in the shells of this (No. 7) and the stratum (No. 6) immediately above it — namely, that the large Trigonioe are wanting, although there are numbers of the smaller kind, and young individuals. Future investigations will perhaps modify these conclusions. The Hamites and Modiola, from which I have named the zone, may be found to extend into others in reduced numbers ; but in this particular zone they have a great numerical superiority.
In the bed marked 6, the same type of shells appears as in No. 7. The rock is also apparently of the same kind. But only a few small fragments of Hamites are found ; and in the bed above, marked 5, the Hamites seems to have disappeared entirely, and apparently all the peculiar shells that accompanied it — their places being supplied by others of a different character. Amongst these the principal is the beautiful Trigonia ventricosa. It abounds here, and is, in fact, the characteristic fossil of the bed in this particular locality. A few isolated specimens have been found in the Zwartkops strata ; but here they are, in some places, massed together in thousands, outnumbering every other shell. Trigonia vau is also very abundant ; and hence, in the general Section (fig. 3), I have called this (No. 5) the Trigonia-ventricosa- and T.-vau-zone. Fine specimens of Gervillia dentata also have been obtained from it, together with Exogyra imbricata, Pecten Rubidgeanus, and Turbo Stowianus.
In bed No. 4 the Trigonioe, compared with those in No. 5, are not only very much fewer and smaller, but, from some alteration of circumstances, apparently were disappearing from this part of the ancient ocean. The remains of other shells are also far less abundant than in the lower zones. The sandstone above No. 4 is much altered in character compared with those underlying it, being, as I have before remarked, less compact, and far more coarse and friable than those below. This difference of texture increases the nearer we approach the upper portion of the section, where the sandstone seems to assimilate in lithological character more to the upper sandstones of the Koega, and to those interlaminated with the dags at the Bethelsdorp Saltpan (see further on), than to any others.
Immediately above these, as shown in Section E (fig. 3), is a shell- bed, from 3 to 5 feet thick, composed of small fragments of shells, thickly interspersed with a species of Ostrea. This stratum seems to be of Pliocene or Postpliocene age, and to be the equivalent of the upper shell-limestone on the Zwartkops and the Koega. Above this, again, is a conglomerate, varying from 3 to 6 feet in thickness. This is capped with tufaceous limestone, from 2 to 3 feet thick ; and above the limestone is a red, sandy, marly clay, varying, according to the inequalities of the surface, from 4 to 6 feet. I send a sketch of the bluff (fig. 2), the better to show the formation.
