Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/703

 gradual lowering of the temperature of the more southern parts of this coast since the limestone was deposited.

During the formation of the shell- banks in the Zwartkops estuary, younger than the Pliocene limestone, the immense number of certain species of shells, which have as yet been found living only in latitudes nearer the equator, point to a somewhat similar though a more modified change of temperature.

These, however, do not seem to have been the only periods when this part of the world had a temperature different from that it now possesses. In the Jurassic times the shells of the Trigonia-be&s indicate a tropical or subtropical climate.

Nor are evidences wanting that there must have been vast intervening periods when the climate approached to something like antarctic severity. A question worth asking is, What can have been the cause of the enormous accumulations of conglomerate at Enon, at the sources of the Zwartkops, at Hankey, and elsewhere ? Dr. Atherstone thus writes * of this formation at Wit- water river : — " the whole range of hills was actually formed of these rounded pebbles;" "the further we went the higher the cliffs became;" " a red clay formed the cement which bound them together ;" "cliffs 200 or 300 feet high." In the Kloofs at the sources of the Zwartkops this conglomerate is described by him as " piled up 300 or 400 feet high;" at Venster - Hoek, Hankey, it is "740 feet high," " composed entirely of this Enon conglomerate," with a matrix of " soft red sand."

Surely this enormous accumulation of water- worn pebbles† was brought about by no common action of the sea-waves and ocean- tides ! but rather by the piling-up of worn fragments of rock on a stormy ice-bound coast under an extreme condition of climate‡.

Configuration and origin of the Karoo Beds. — During the last few years I have had several opportunities of examining portions of the Katberg and Stormberg ranges ; and in many places they give (as far as I can judge) strong evidences of having been subjected at a remote period to the force of ice-action, and, indeed, that this has been the great denuding agent of the Dicynodon-strata. After a residence of nearly six years, the conviction has been forced upon me that this denudation can be attributed to nothing else than to the action of glaciers through an incalculable period of time. It seems almost impossible that ordinary atmospheric agencies could have eroded the surface so deeply and extensively, and carried away vast tracts of strata that not only once occupied the area of the wide plains and valleys now extending between the different branches of


 * Eastern Province Magazine, vol. i. (1857), p. 523 &c.

† The "Enon Conglomerate" has also been noticed by Bain and Atherstone as occurring in the George district, Cape of Good Hope. — T. R. J.

‡ The suggestion of Dr. Sutherland that the great breccia-band at the base of the Karoo formation in the Cape Colony and Natal is a boulder-clay of glacial origin (Quart. Journ. Geol. Soc. vol. xxvi. p. 514), is consonant with this view of a severe antarctic climate having again and again obtained in South Africa. — T. R. J.