Some scientific results of a mission to South Africa / by Professor Seeley.

  • Harry Govier Seeley
Date:
1889
Catalogue details

Licence: Public Domain Mark

Credit: Some scientific results of a mission to South Africa / by Professor Seeley. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    2/16 page 2
    in which the rocks have been crushed together laterally by this intense power coming from the south. And when I had passed through this range (where I found the ancient limestones completely cry- stallised, limestones which themselves have been worn into pebbles and laid down as sure deposits, cemented into marble, which pebbles had acquired crystalline structure,) then upon these marbles I found altered rocks, ancient clays greatly altered, now converted into the condition of cleaved slates by the pressure, and upon this sandstone, rested and changed into quartzite, stones formed of pebbles in the same way, rolled down ancient shores, which pebbles were themselves bound together by a cement, formed in consequence of the intense heat, due to the process of compression. I then turned towards the rocks in the Prince Albert region, to those newer rocks which rest upon the Zwartberg, and which form the base of the series which we know as the Karoo rocks. Now what those lower beds may he which intervene between Prince Albert and Zwartberg, I will not now stop to discuss, but I will say that just to the south of Prince Albert you come upon a marvellous rock which has amazed every one who has examined it, and defied the skill in interpretation of every one who has brought the powers of the microscope to bear upon it, and that rock we know as the Ecca conglomerate, which was sometimes called by your earlier geologists, (especially by Mr. Andrew Bain, that wonderful genius to whom we owe the first interpretation of the geological structure of Africa), the trap con- glomerate, and presents the aspect of a trap on the one hand, and a conglomerate on the other. But when we come to consider what variance there is in these terms, that a trap means a lava flow forced out from a volcanic centre flowing over the surface of a country, and that a conglomerate means a rock rolled into the form of pebbles by the action of the breakers on shore, which boulders have sub- sequently been united by some kind of cement, you will see that the old name of “ trap conglomerate ” implies such a contradiction that in the interests of science we lay it one side, fully recognising the dis- crimination which recognised its true character, and we adopt the name “ Ecca conglomerate ” instead. Now by this term Ecca con- glomerate, which I believe we owe to Mr. Dunn, we mean a rock in which you find rounded boulders and angular fragments of all kinds of rock, for the most part crystalline, and very frequently perfectly altered from their original condition, and embedded in a cement which resembles different forms of volcanic ash (ash such as that which was thrown out in the wonderful eruption of Krakatoa), which apparently fell upon a shore where pebbles and boulders were brought down in great quantity, and which have become cemented into a rock, which now, after the long lapse of ages, presents the aspect of a trap,
    No text description is available for this image
    No text description is available for this image
    No text description is available for this image