CLIMATES OF GEOLOGIC TIME—SCHUCHERT. 309 - 
It has long been known that during times of intensive mountain- 
making and more or less cooled climates there was great destruction 
and alteration of life. The first effects of the environmental changes 
occurred among the organisms of the land, while the climax of altera- 
tion among the marine life appeared later. This is especially well 
seen in the Permic glaciation, which first blotted out the cosmopolitan 
Upper Carbonic flora and the insects, while the life of the sea con- 
tinued without marked change into Middle Permic time. In the 
later Permic, in the northern equatorial waters of Tethys, occurred 
the final destruction of many stocks that had long dominated the 
Paleozoic seas. The explanation of these facts appears to be that on 
the lands the change of climate takes immediate effect on the organ- 
isms, while in the oceans a longer time is consumed in cooling down 
the warm and equable temperature and in filling all the basins with 
cold water. Accordingly the last regions in the oceans to come under 
the influence of glacial climates must be the shallow waters of the 
equatorial area. The proof of this conclusion is seen in that the last 
stand made by the marine Paleozoic world is recorded in the deposits 
of Tethys, the great Mediterranean sea of Permic time. It is also 
here that we find nearly all of the Paleozoic shallow-water holdovers 
in the succeeding period, the Triassic. 
The cooled but not frigid climate that followed the magnificent 
mountain making at the close of the Cretacic also produced striking 
changes in the organic werld. These changes were less marked than 
those of Permic time and more noticeable among the land animals 
than those of the marine waters, affecting especially the overspe- 
cialized, large, thick-shelled, and degenerate stocks. 
Great changes were again produced among the large land animals 
of the world, as well as among those of the polar and temperate 
oceanic waters, by the glaciation of Pleistocene time. The present 
shallow waters of the equatorial region still maintain the late Tertiary 
faunas, and Africa is the asylum where the higher Pliocene land ani- 
mals have been preserved into our time. 
What the effects of the Proterozoic glacial climates were upon the 
living world of that time it is impossible to say, because we have as 
yet discovered but little of the organic record. 
The marine “‘life thermometer” indicates vast stretches of time of 
mild to warm and equable temperatures, with but slight zonal differ- 
ences between the equator and the poles. The great bulk of marine 
fossils are those of the shallow seas, and the evolutionary changes 
recorded in these ‘‘medals of creation” are slight throughout vast 
lengths of time that are punctuated by short but decisive periods of 
cooled waters and great mortality, followed by quick evolution, and 
the rise of new stocks. The times of less warmth are the miotherm 
and those of greater heat the pliotherm periods of Ramsay (1910). 
