THE TEANSAOTIONS 



OF THE 



c^owi^-g^friatt Jj^ikso^^iml ^oddis. 



NOTES ON THE GEOLOGY OF THE COAST BETWEEN THE 

 FISH AND JUJA EIVEES, SOUTH AFEIOA.— By 

 George McKay (communicated by John G. Gamble, M.A.). 



[Eead 1884, March 26.] 



Part I., Igneous Eocks. 



Though the writer proposes to deal with the surface or newer 

 geographical features only, it will be necessary — in order that he may 

 clearly carry the reader with him — to run rapidly over some of the 

 older formations that have an important bearing on their successors. 

 In this paper, therefore, the writer devotes his remarks exclusively to 

 one class of rocks, viz., the igneous; reserving to another time the 

 consideration of the sedimentary formations and the superficial 

 accumulations. 



Every one acquainted with the geology of South Africa is aware of 

 the very remarkable formation known as the ''trap conglomerate," 

 which, shewing itself on the east coast between the 33rd and 34th 

 degrees of south latitude, trends in a westerly direction for hundreds 

 of miles, till it turns north and becomes lost among the metamorphic 

 rocks of Namaqualand, everywhere maintaining a character so 

 uniform and peculiar as to make its recognition an easy matter to any 

 one acquainted with the subject. The formation is also important 

 from the fact that it marks the northern boundary of the paleeroic 

 rocks in the southern part of the Colony. For these reasons it has 

 been selected as the starting point of this paper. 



The principal band (there are several) of the trap conglomerate is 

 well seen at Stalwart Point, near the Fish Eiver, where it forms the 

 eastern horn of Waterloo Bay. This shallow inlet owes its formation 

 to the greater endurance of the ''trap conglomerate " and the angle 

 which it presents to the great swell of the southern ocean. A refer- 

 ence to the maps will show that most of the igneous rocks form small 

 promontories on the coast. It is not intended to enter on the difficul- 

 ties that surround a satisfactory solution of how the trap conglomerate 

 was formed. In the following remarks the reader is supposed to be 

 travelling eastward from Stalwart Point along the coast between high 

 and low water marks— the position most favourable for ascertaining 

 the nature of the rocks travelled over. On arriving near the mouth of 

 the Bequa Eiver he will find another, though much smaller, band of 

 trap conglomerate. It forms what is called the " Madagascar Eeef " 

 on maps. Whatever difficulties there may be in accounting for the 

 peculiar contents of the trap conglomerate, if they be assumed to be 



