1877.] Catastrophism and Evolution. 459 
of the great oceans. The whole history of the Tertiary is that 
of the accumulation of thick sedimentary series in fresh-water 
lakes, accompanied by gradual and periodic subsidence, carried 
on smoothly and uniformly up to a certain point, and then inter- 
rupted by a sudden, mountain-building upheaval, which drained 
the lakes and created new basins. The five minor catastrophes 
which have taken place in the western half of America during 
the Tertiary age have never resulted in those broader changes 
which mark the close of the Archean, the Paleozoic, and the 
Mesozoic ages. They never broke the grander outline of the con- 
tinent. They were, however, of such an important scale as to 
very greatly vary the conditions of half the continent. I may 
cite the latest important movement, which took place probably 
within the human epoch, certainly at the close of the great Plio- 
cene lake period of the west. The whole region of the great 
plains, as far north as we are acquainted with their geology, and 
southward to the borders of the Gulf, was occupied by a broad 
lake which existed through the Pliocene period, having always a 
subtropical climate. In that lake, beds 1000 to 1200 feet thick 
had accumulated, when suddenly the level floor was tilted, caus- 
ing a difference of height of 7000 feet between the south and 
west shores, making the great inclined surface of the present 
plains, and utterly changing the climate of the whole region. 
Not a species survived. 
I have thus hastily mentioned a few of the most important 
geological crust changes in America whose rates are demonstrably 
catastrophic. Besides surface changes involving subsidence, up- 
heaval, faulting, and corrugation, all of which may be executed 
on a scale or at a rate productive of destruction of life, catastro- 
phes may be brought about by sudden great changes of climate 
or by intense volcanic energy. In the latter field there are 
obviously no catastrophes of the first order. Geological maps 
of the globe have progressed far enough to demonstrate that con- 
siderable areas are, and always have been, free from actual ejec- 
tion of volcanic materials. On the contrary, numerous great re- 
gions, notably the western third of our own continent and the 
Shores of the Pacific, were once literally deluged with volcanic 
res. An examination of the ejected rock shows that modern 
eruptions, by which the volcanic cones of the present period are 
slowly built up from slight overflows piling one upon another, are 
not the method of the great Miocene and Pliocene volcanic peri- 
ods. There were then outbursts hundreds of miles in extent, in 
