476 TRANSACTIONS OF SECTION ©. 
mountain-land and of the sea-basin admitted of the accumulation of a temporary 
lake. Post-glacial erosion and subsequent changes of level have completed the 
bed of the strait as it now exists. 
2. The Origin of Kopjes and Inselberge. By J. D. Fauconrr, M.A., 
D.Sc. 
Detached hills, projecting crags, and isolated rocks are features of almost 
every landscape, and in the moister regions of the globe their origin has usually 
been correctly assigned to the ordinary processes of denudation. They may 
arise either through the dissection of earlier plateau-surfaces, as frequently in 
the case of detached flat-topped and pyramidal sandstone hills, or by the 
weathering out of the more resistant units where the surface is composed of 
rocks of different degrees of hardness, as in the case of escarpments and of 
detached crags and hills of igneous rock. The kopjes and island mountains of 
the warmer temperate and tropical regions are essentially of similar origin, but, 
on account of the present climatic conditions being in many cases different from 
those under which they were formed, their actual mode of origin has given rise 
to considerable discussion. A striking feature of these kopjes and inselberge is 
that they rise at intervals from an apparently level or gently undulating plain, 
which in most, if not all, cases should be regarded as a former base-level of 
erosion. The typical kopjes of South Africa are of sandstone, shot with veins 
and dykes of igneous rock, which has given them the necessary power of resist- 
ance to the agents of erosion. The old crystalline regions of Africa, however, 
are dotted with domes and turtlebacks of granite and detached groups of 
granite hills, which represent the more resistant elements of the crystalline 
complex. Some of these isolated hills possess flattened caps of weathered rock, 
and it seems probable, therefore, that the sculpturing of the original crystalline 
surface was due, not so much to the direct erosion of the unweathered rocks, as 
to the effect of periods of elevation and erosion following upon periods of decom- 
position in situ at base-level. As the result of erosion a somewhat irregular 
surface would be produced, but a slight subsequent negative movement would 
suffice for the obliteration of the minor irregularities and the consequent accentu- 
ation of the less weathered portions of the surface. The repetition of such a 
cycle would lead to the increased prominence of the earlier hillocks and the 
formation of others of lower level. It has been suggested that a landscape with 
inselberge is of desert origin, but the various phenomena can be explained more 
readily as the result of weathering and erosion during successive small oscillatory 
movements of a regional character in the neighbourhood of base-level. 
3. Note on the Country North of Lake Albert. 
By G. W. Grasyam. 
4, Secondary Quartz on Pebbles. By G. W. Grasuam. 
5. Post-Glacial Changes of Level versus Recent Stability of the Lake 
Region of America. By Dr. J. W. SpENcER. 
About the lake region extensive beaches, now raised, have their former 
water-levels deformed by rising towards the north and east. The tilting was 
recognised as early at 1851 (by Professor Stoddard) to have been due to earth 
movements. 
At the period referred to the lakes were larger than at present, and differently 
grouped, forming Lakes Warren, .\lgonquin, and Iroquois, discovered and named 
by the author. From their abandoned shore-lines it is found that between the 
head of Lake Ontario and a point near its outlet (at Watertown, N.Y.) there is 
a rise of land from 363 to 730 feet above sea-level, or 367 feet. If the uplift be 
ee from the head of Lake Erie to the same point (400 miles), it amounts to 
507 feet. 
Calculating the mean direction in various triangles, the change is found to be 
reduced to almost zero at the head of Lake Erie; two feet per mile, N. 22° E., 
