THE QUIZZYHOTA LACCOLITE gI 
THE CHANNELS BY WHICH THE ACID RESIDUES ESCAPED 
The escape of siliceous material from the dolerites should leave 
somewhere some trace. As the channels of supply function at the 
same time as conduits for the waste material, there should exist 
occasionally composite dykes of the type described from Canada 
by Lawson,’ and from Norway by Vogt,? which have basic margins 
and granite or syenite centers. Similar ones occur in Arran con- 
sisting of selvages of augite-andesite and centers of quartz-felsite 
as described by Judd. They have also been found in Skye and the 
Thiiringer Wald.4. No dykes of this nature have so far been noticed 
in South Africa, but diorite dykes genetically related to the dolerite 
sills are fairly common about Cradock and Kentani. A pair of 
parallel dykes in the Transkei were described by Dr. Rogers and 
myself in rg901; they run a little north of the Quizzyhota, cross the 
Kei, and traverse the Kentani district to its eastern border along 
the Kogha River; the easy weathering of this rock as compared to 
that of the dolerite and Karroo sediments has left deep furrows in 
the land, which have been given the local name of the “Transkei 
Gap.’s Another diorite mass occurs at Gonubie along the main 
road from Kei Road to Komgha. The Gap-rock was described 
by Dr. Rogers in the paper referred to, and I reproduce it for com- 
parison with the description of the dolerite of the Quizzyhota. 
The rock forming the dykes of the Gap is a peculiar one, differing in 
important respects from any intrusions hitherto found by us in the Karroo 
Formation, although as will be pointed out in the following notes, it has a 
distinct relationship to the olivine-dolerite of the sheets.6 It consists chiefly 
of the following minerals in the order of their usual relative abundance: plagio- 
tA. C. Lawson, Report on the Geology of Rainy Lake Region, Geol. and Nat. Hist. 
Survey, Canada (Ann. Rept., 1887-88), Part F. 
2J. H. L. Vogt, Geol. Mag. (1892), 82; W. C. Brogger, Eruptivgesteine des Kris- 
tianiagebietes, I (1894), 56. 
3 J. W. Judd, ‘‘Composite Dykes in Arran,” Q0.J.G.S., XLIX, 545 ff. 
4A. Harker, Tertiary Igneous Rocks of Skye, chap. xii. 
5 A. W. Rogers and E. H. L. Schwarz, ‘“‘The Transkei Gap,” Trans. Phil. Soc., S. 
Africa, XIV. (Cape Town, 1901), 63. 
6 The olivine-dolerite which forms the intrusive sheets of the Transkei is very like 
the rocks occurring in the same manner near Beaufort West, and described by E. 
Cohen, Neues Jahrb. (1874), 195. 
