Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/680

 kops. Again, as a proof that their position is below the Zwartkops Trigonia-beds, it has been stated that these saliferous rocks are found resting unconformably on the quartzite and clay-slate, in the direction of Bethelsdorp and Chatty. But, again, this of itself is no proof; for near the Shark's River one of the most recent shell- deposits also rests directly on the quartzite.

Dip. — We will therefore first enter into the question of dip, especially that of the Government Saltpan — in the first place, however, premising that between this Pan and the saliferous deposits of Bethelsdorp and the neighbourhood of Port Elizabeth the strata of the Zwartkops, as shown in sections B & C intervene. The Pan itself is in a denuded depression ; but this hollow is not very deep, as is indicated by the rising ground that surrounds it, and from the top of which a plateau stretches on the same level as the upper edge of the Zwartkops Heights — in fact, is continuous with them, as is seen at d' in Section B, (fig. 7).

Dr. Atherstone * says that the strata at Geelhoutboom dip S.W., towards the centre of the ancient estuary, at an agle of 8°, and those of the Zwartkops conversely N.E. ; and he gives the dip of the Saltpan rocks at the same angle to the north-east, that is, in the same direction as those of the Zwartkops. Now it is certain that for a number of miles together the dip of the Zwartkops strata continues with great uniformity at nearly the same angle. But an angle of 8° gives a depression of about 1 foot in 15 ; and if continued two miles (about the distance of the Government Saltpan from the top of the Zwartkops Heights), there would be a total fall of some 1500 feet. The highest hills anywhere in the neighbourhood are the Koega Kopjes ; and they are only 480 feet above the level of the sea. The depression of the Saltpan is certainly not 300 feet below the level ef the Amsterdam Flats, the plateau from which these Kopjes rise, as that would place it below the level of the sea, which it decidedly is not ; but, even allowing it to be so, the angle given would place the Zwartkops sandstones, if they extended as far as the saliferous strata of the Saltpan (which I think is not doubted), 1200 feet below them. A dip of 4° (the same as at Rocke's Bluff) would allow rather more than 700, or some 400 feet below : and even the small angle of 2° would still leave the Trigonia-beds between 70 and 80 feet lower than the deposits of which I am speaking.

Fossils. — At the Government Saltpan (p. 505) Dr. Atherstone has found Trigonioe and Turritelloe associated with Ostreoe and Cidaris pustulifera. I cannot help thinking that this is the oldest portion of the saliferous strata that has been yet examined. The stratified clays of the Bethelsdorp Pan and those at the Salt Vlei are, I believe, more recent. At the former of these Cidaris and Ostrea are abundant ; but no Trigonioe are yet known there ; while at the latter spot no specimens of either the one or the other have been obtained, although Cidaris has been found on the sides of the outlier (Section O, fig. 4) on the east of the Vlei. This outlier, I believe,


 * Loc. cit. p. 581, and woodcut, no. 1.