180 The American Geologist. February, 1894 
Reade, and the isostatic theory of Dutton. When it is necessary to ac- 
count for the compression of vast masses of rock into a third of their 
normal dimensions and for their elevation thousands of feet above the 
level of the sea we may be thankful to invoke all available powers, each 
in its proper place, and the sculpturing due to atmospheric agencies 
besides. 
This led to a consideration of the uniformitarian and catastrophic 
theories. While on the one hand geologists are consistent in holding to 
the constancy of the laws of nature and the uniformity of their action 
in kind, on the other hand a catastrophe is often merely the culmina- 
tion of slowly acting causes and is truly a part of the uniformity of na- 
ture. The slow crumbling of the face of a cliff is very gradual, but it 
leads to the sudden fall of vast masses of rock, exposing again new sur- 
faces to intinitesimally slow decay. 
He next referred to the slow and gradual accumulations of organic 
matter as causes and effects of change. He instanced the growth of 
the coal measures and the relation of this to the gradual subsidence of 
continental areas, and showed that coal of the ordinary kinds, not in- 
cluding cannel, is a product of subaerial accumulation of vegetable 
matter, under peculiar conditions, which recurred in various geological 
periods, but most extensively in the Carboniferous era. 
Another subject of much interest in connection with the same gen- 
eral matter is the evidence afforded by fossil plants as to the changes of 
climate and the geographical causes thereof. He showed by many il- 
lustrations how much light fossil plants are capable of throwing on 
these questions and how strongly they support the idea that the vicis- 
situdes of climate in geological time are mainly due to the different 
distribution of land and water. In connection with the same subject 
he showed that the areas qf land and water have been sufficiently sta- 
tionary to support a continuous succession of animal and vegetable life. 
Much light is thrown on the vexed question of the refrigeration of the 
northern hemisphere in the Glacial period when we learn that the ice 
of this period is local rather than general, and that local glaciers of 
great magnitude on elevated ground and depressions of lower lands be- 
neath the sea were mainly responsible for this icy episode. Sir William 
held that no one cause can explain the phenomena of this great refrig- 
eration, but that changes of level and of ocean currents were dominant, 
that areas of evaporation as well as of condensation were required, and 
that the succession of deposits can be explained only by a consideration 
of the changes of physical geography in the successive stages of the 
period. 
He further directed attention to the evidences of an open polar sea 
throughout the Glacial period, of the great submergence of the land 
during this time, and of the necessity of abandoning the attempt to ac- 
count for all of the phenomena by the action of land ice, since we must 
recognize the effects of sea-borne ice as well as of glaciers. He referred 
to the evidence now available as to the recency of glacial times and the 
arguments which suggest vast movements of the earth's crust in periods 
geologically modern. 
The speaker then noticed the opinions lately advanced by a number 
of leading geologists as to the probability of a great diluvial catastrophe 
since the advent of man on this globe. He had himself long advocated 
the necessity for such an occurrence, on the evidence of the extension 
of the northern continents in the early human period, and the appar- 
ently sudden destruction of men and many of the larger animals of the 
Palanthropie age, producing a vital hiatus between this and the suc- 
ceeding ages. 
This conclusion seems now triumphant and is beginning to bring the 
geological events of the later Tertiary into harmonious connection with 
the history of early man as deduced from our traditions and records. He- 
