
100 STRUCTURAL AND FIELD GEOLOGY 
Carboniferous period could not have flourished under arctic 
or even cold temperate conditions of climate; and we may be 
equally convinced that the abundant corals and cephalopods 
of Palzozoic times, with their numerous congeners, were not 
denizens of cold seas. Existing conditions might even lead 
us to believe that the massive limestones of those early ages 
were most likely formed in genial waters. For at the present 
day it is in warm seas that lime-secreting organisms, such 
as corals, pelagic molluscs, and foraminifera, flourish most 
abundantly, and are there giving rise to widespread and thick 
accumulations of calcareous matter. But whether the climatic 
conditions of Paleozoic times were similar to those of our 
present warm latitudes, it would be rash to conclude. 
When the geographical distribution of Paleozoic floras and 
faunas, however, is kept in view, we may advance our 
inferences a step further. Should the fossils or groups of 
fossils of some particular formation be known to occur over 
vast areas of the earth’s surface, in arctic, temperate, sub- 
tropical, and tropical latitudes, and even in similar latitudes 
of the Southern Hemisphere, we should be justified in the 
inference that the climatic conditions indicated by the fossils 
in question must have been singularly equable. ‘The mere fact 
that in the earlier stages of the world’s history, cosmopolitan 
forms of plant- and animal-life abounded, affords good ground 
for believing that the climatic conditions of those far past 
times differed considerably from the present. The climate of 
the globe in those days could not have been differentiated 
into such distinct zones as is now the case. 
Geographical Conditions deduced from Fossils.—Fossils 
naturally yield evidence as to terrestrial, freshwater, and 
marine conditions. 
(a) Land-surfaces—These are seldom preserved. Never- 
theless, they do occur in strata belonging to widely separated 
periods. Now and again, for example, the stools and roots 
of trees penetrating ancient soils, occur interbedded with 
sedimentary strata, a good example being furnished by the 
“dirt-bed” of Portland. This dirt-bed is simply an old soil 
containing the roots and stumps of extinct forms of cycads 
and conifers. It is intercalated between beds of freshwater 
origin, a succession which shows that, after the deposition of 
