THE, QUIZZYHOTA LACCOLITE 79 
till detritus from land could no longer reach the particular locality ; 
at the same time, owing to the violence of the currents or the cold- 
ness of the sea or for some other cause, the calcareous deposits in the 
deep ocean did not form, or, if they did form, were dissolved. Then 
when the sea-floor rose again and the shore advanced, sedimenta- 
tion began once more, and the new deposits were laid down con- 
formably on the older ones, although a considerable lapse of time 
had occurred between the two.' In the per saltem conformity 
between the Umsikaba and Idutywa Series we have other considera- 
tions to take into account. We are dealing with fresh-water 
deposits. In the Cape Colony proper, that is to say, in the central, 
south and west portions of the Great Gondwanaland Lake—Lake 
Union we might call it, as it embraced all the colonies united in the 
Union of South Africa, whereas the Karroo sediments of Rhodesia 
and farther north appear to have been deposited under independent 
sheets of water—the depth was greater and the sedimentation more 
extensive in the early Karroo times. This portion then filled up 
and the depression shifted up to the north and east. The hinge 
of the movement, if we can conceive the lake floors in the two periods 
as forming two planes meeting along a straight line, would run 
through Umsikaba (Flagstaff) in Pondoland and the deposits of the 
earlier depression would then be restricted to irregular arms and 
bays of the older lake and would form discontinuous pockets, as 
indeed they appear to do. 
THE RELATIONSHIP OF THE DOLERITE TO THE SEDIMENTARY BEDS 
It has been necessary to go into a little detail with regard to the 
sedimentary beds around the great Quizzyhota laccolite, because 
I seek to prove in the sequel that the dolerites are in part the 
product of the melting and absorption of the sedimentary beds. I 
have for many years been looking for a good example to work on, 
but there have been objections to all of them. The ordinary dykes 
of the Karroo are of no use, as it is impossible to prove that the 
space occupied by the igneous rock has been melted out by the 
dolerite. Immense laccolites occur in the center of the Karroo 
tE. H. L. Schwarz, “South African Palaeozoic Fossils,” Records Albany Museum, 
Vol. I, Grahamstown (1906), 360. 
