4 Mr. IIcKa?/, Notes on the Geology of the Coad [March 26, 



known of the trap rocks in the Karroo districts of the colony, I 

 am encouraged to offer what have suggested themselves to me as the 

 salient points connected with them, with the hope of receiving corro- 

 boration or correction from other observers. 



1st. They are more recent than the Dicynodon Beds (Lower 

 Triassic of Europe). 



2nd. They do not occur to the south of the line of trap con- 

 glomerate. 



3rd Their numbers are very great (in the proportion of one to 

 every three miles of lineal space). 



4th. They traverse great distances (hundreds of miles) in a 

 perfectly straight line, have a remarkable parallelism to each other, 

 and are of a magnitude unprecedented in any record that has come 

 within my knowledge. Most of the works that I am acquainted with 

 treat the subject incidentally, and I know of no attempt to trace a 

 dyke to its termination. They are usually treated as emanations from 

 some centre in their immediate neighbourhood, or regarded as mere 

 veins. Though beyond the range of the accompanjdng plans, I will 

 here note my attempt to trace a dyke over a very considerable space of 

 ground. This may for convenience be called the " Spitzkop Dyke." 



(a) Between three and four miles north of the Bashee river mouth 

 there is a large dyke of dolerite. A scrubby bush growing on loose 

 sand approaches down to high water mark, and obstructs a view of 

 the direction of the dyke. 



(b) But seven miles from the sea shore a dyke similar in mineral 

 composition crosses the Bashee just above the lowest bridle drift. It 

 is there nearly vertical, and has a trend of 37 deg. west of magnetic 

 north — or corrected for variation 8 deg. north of true west. 



(c) Close to Txakxa— a mission station in the Idutchy wa Keserve, 

 in the Transkei — there is a similar dyke trending 37 deg. west of 

 magnetic north. 



(d) A dyke traversing the Xolosa mountain — between the Tsomo 

 and the Kei Kivers — has precisely the same trend. From the top of 

 this mountain an uninterrupted view eight miles long can be had of 

 this dyke. 



(e) About two miles south of St, Mark's — there is a dyke of dolerite 

 trending 37 deg. west of magnetic north. 



(f ) The Queenstown railway crosses a dyke at nearly right angles 

 one and a-hilf miles beyond (north) Tylden. 



The foregoing six points are from personal observation. In exten- 

 sion of this, a dyke that passes through or close to the town of 

 Tarkastad is described as having a north-east and south-west direction. 



(g) The summit of the Doornberg, in the division of Cradock, is cut 

 through by a dyke, but up to date I have not been able to learn the 

 direction it takes. 



(h) The Spitzkop of the Compass Berg, in the division of Graaff- 

 Reinet, was ascended by AVyley in 1857. He describes the dyke that 

 intersects the peak as cutting the perpendicular south-west face at an 

 angle of 50°. This description, though not as precise as could be 

 desired, leaves little doubt that the dyke there takes the same general 

 direction as the other points, that have their trends fixed, do. Now 

 if the reader will plot these points on a fairly good map, it will aiford 

 a strong presumption that the Spitzkop dyke forms one continuous 

 and direct line to the Bashee mouth, a distance of upwards of 260 miles. 



