Reports and Proceedings—Geological Society of London. 331 
earth-movements in late Carboniferous times: these threw the forest- 
bearing surface into shallow waves and troughs, which became 
gradually accentuated, the latter being gradually filled with sediment, 
upon which, during intervals of rest, new forest growth took place. 
2. ‘* Petrological Notes on the Igneous Rocks lying to the South- 
East of Dartmoor.”’ By Harford John Lowe, F.G.S. 
The rocks described are contained in the Newton Abbot district, 
the region east of the Dart and south of the Teign. They are most. 
nearly related, both geologically and petrologically, to those of South- 
West Devon, or the Plymouth district described by Worth. The 
numerous intrusions occurring in the Devonian and Culm rocks have 
been summarized by Dr. Teall as ‘‘for the most part referred to the 
basic kind known as diabases.”” The Ashprington rocks are finer 
grained and lighter in colour than those of the other groups: the 
Newton Devonian specimens range from light greyish-green to nearly 
black, and in texture from fine to medium; while the Culm specimens 
are nearly all of coarser texture, occasionally mottled, and on an 
average of slightly darker shade. The masses of igneous rock in the 
district do not display such evidence of extreme dynamic stress as is 
found among the related rocks farther west. The rocks described 
from the Devonian voleanic group include tuffs, basalts, and diabases 
(mostly free from olivine, though there are exceptions), picrite, 
leucophyre, and kersantite. ‘The Culm volcanic rocks show an 
absence of the finer-grained basaltic class, as well as some distinct 
difference in mineralogical constitution of the most nearly allied, 
indicating subjection to different physical conditions. The rocks 
include tuffs, diabases, proterobases, epidiorites, camptonites, 
teschenites, hornblende diabases, mica-lamprophyre, and porphyry. 
II.—May 15th, 1907.—Sir Archibald Geikie, D.C.L., Sc.D., Sec.R.S., 
President, in the Chair. 
The following communication was read :— 
“On the Origin of certain Caiion-like Valleys associated with 
Lake-like Areas of Depression.” By Frederic William Harmer, 
F.G.S., F.R.Met.8. 
In glaciated regions, as shown by Professor P. F. Kendall, the 
invasion of a district by an ice-sheet would tend to obstruct the 
natural drainage, producing lakes, of which the outflow might take 
place over the advancing ice, between the ice and the hillsides; or 
it might escape laterally, in a direction at right angles to the longest 
diameter of the lake and to the course of the pre-existing stream. 
Overflow channels would assume a gorge-like character, and would 
present a comparatively recent appearance. During the Glacial Epoch 
the North Sea ice appears to have invaded the plain of the Witham 
and the valleys of the Welland, Nene, and Ouse, overriding also the 
higher land separating them; the Tees ice-stream moved up the 
Trent basin to the vicinity of Derby and thence, inosculating with 
the Derwent glacier, up the Soar» Valley towards Leicester and 
