The Sutherland Volcanic Pipes. 81 



differences there is such a close general resemblance between the 

 rocks from these different localities, and the type of rock is such an 

 unusual one, that there is reason to believe them to have been con- 

 nected in their origin. Beyond the community of type and manner 

 of occurrence there is at present no evidence to bring forward in 

 support of this view, which is, therefore, to a large extent hypotheti- 

 cal. As to their relative ages there is not much evidence ; the 

 Sutherland pipes are younger than the Karroo dolerites, and there- 

 fore very probably younger than the Stormberg period, but how 

 much so is an open question ; the Spiegel Eiver intrusion took 

 place later than the deposition of the Uitenhage beds, or rather than 

 that portion of them represented in Kiversdale. The Stormberg 

 beds may be considered as of upper Triassic (Ehaetic) age, and the 

 Uitenhage beds are correlated with the Lower Cretaceous of Europe. 

 If the supposition of a common origin of the Spiegel Eiver and 

 Sutherland pipes can be legitimately made, then the latter must 

 also be considered as of later age than the Uitenhage period. 



General Summary of the Eelationship of the Volcanic Vents. 



There is good reason to think that the peculiar pipes, filled with 

 breccias of various kinds or with ultra-basic igneous rock, found at 

 so many places within the Colony, near Pretoria, and in the Orange 

 Eiver Colony were produced at about the same time. Though the 

 pipes at present known occur in groups far removed from one 

 another, it is probable that many more have escaped detection, or 

 have been found unprofitable by prospectors, and therefore have 

 passed out of memory. The fragments of blackened wood dis- 

 covered in the blue-ground at Kimberley probably came from trees 

 growing near the vent at the time of the explosions, and are the 

 only direct evidence of the area having been dry land at that time. 

 By other arguments, however, we may be satisfied that the eruptions 

 took place after the great fresh-water basin in which the Karroo 

 formation was deposited became dry land. This event probably 

 happened at the close of the Stormberg period, and there is no 

 evidence of the deposition of any later beds, save gravel and allu- 

 vium, in the Karroo region. Whether the Uitenhage beds extended 

 into this area is not known, but in any case it is not likely that they 

 ever formed such thick bodies of rock there as they did south of the 

 Zwartebergen. We may consider that since Stormberg times the 

 great interior region of the Colony has remained above the level of 

 the sea, and at some time during the long epoch that separates the 

 present day from the Stormberg (Ehaetic) period, the terrific ex- 



