578 TC: CHAMBERLIN. 
species in different latitudes clearly indicates that they are less 
abundant in the arctic provinces than in the tropical, from which 
it may perhaps be safely inferred that the lime-secreting function 
of the mollusks is increased by warm temperature. 
In the foregoing quotations references are made to the 
preference of certain forms for shallow waters. The great pre- 
ponderance of lime-secreting species on the shoal areas— 100 
fathoms or less—is too familiar to need emphasis. 
In other articlest I have endeavored to show that there were 
certain stages in the earth’s history when the seas were extended 
widely over the continental platforms, affording conditions 
extremely favorable to the multiplication of lime-secreting 
shallow-water life. I endeavored to connect these, on an obser- 
vational basis, with the great limestone-producing epochs of 
geological history and to show that these were correlated with 
genial climates over high and low latitudes alike. On the other 
hand, I endeavored to show that there were other periods during 
which the land area was increased and the sea restricted, result- 
ing in a great reduction of this normal habitat of the chief lime- 
secreting forms of life. I endeavored to show that so far as the 
lime-secreting life is concerned, the freeing of carbonic acid was 
promoted during periods of extended seas and that it was. 
retarded during periods of extended land. This holds good 
when considered simply from the standpoint of available area, 
but it becomes still more true if, as this hypothesis maintains, 
the extension of sea-area was correlated with favorable tempera- 
ture, while the restriction of sea-area was correlated with adverse 
temperature. The only pelagic life that enters much into the 
problem is that which occupied the superficial waters of the open 
ocean. The area of this increased and diminished concurrently 
with the extension and contraction of the sea. 
* A Systematic Source of Evolution of Provincial Faunas, Jour. GEOL., Vol. VI, 
No. 6, pp. 597-608. 
The Influence of Great Epochs of Limestone Formation upon the Constitution of 
the Atmosphere, JouR. GEOL., Vol. VI, No. 6, pp. 609-621. 
