548 
SILUBIA. 
of the Carboniferous Limestone. Looking to the general arrangement of the 
chambered structure, I can entertain no doubt that the true Stromatopora, as 
represented by the specimens 3-ou have placed in my hands, is a Foraminiferal 
organism." 
Dr. Carpenter has also carefully examined a portion of the specimen figured 
in Plate XT J. fig. 32 (named ' Stromatopora nimimulitisimilis ' in the Sil. Syst.), 
and he corroborates the statement given in the last edition as to its oolitic 
nature; for he finds it to be unmistakeably pisolitic, being formed of small 
concentric calcareous nodules, imbedded in a matrix consisting of comminuted 
shells and other organisms. 
S. — A New Theory of several former Glacial Periods (p. 505). 
In the concluding pages of this work a brief allusion only has been made to 
what I term the great glacial period, which some geologists believe was divided 
into two epochs, separated from each other by a long lapse of time, during which 
a rich vegetation flourished, and when, according to certain writers, man him- 
self existed. Eecently, however, this theory, founded on the changes in the 
obliquity of the ecliptic, has been ingeniously extended by Mr. Croll to what I 
cannot but consider much beyond its legitimate application when he speaks of 
evidence of ice-action during the Devonian and Silurian epochs ! In fact, great 
length of time being allowed, his theory may be applied during all geological 
periods. 
Now this view is entirely antagonistic, as respects the Palaeozoic eras, to the 
facts and reasoning brought forward in this volume. The wide, if not universal 
spread of the same marine animals during the Silurian epoch, and the similarly 
broad extension of the same land-plants in the Devonian and Carboniferous 
epochs, are all evidences of the then prevalence of a mild and equable tempera- 
ture. In those early periods when the same groups of animals were so widely 
diffused, there could have been no lofty mountains and equivalent deep seas, 
inasmuch as the latter would have operated as positive barriers to such wide 
extension of marine creatures. 
If there did not then exist that great variation of outline which became do- 
minant in the Tertiary times and has increased in our epoch, and if in the 
Palaeozoic ages low or moderately high tracts of land alone prevailed, I have yet 
to leam what cause could then have operated to bring about a great extension of 
glaciers like that which really took place at the close of the Tertiary period, when 
the loftiest mountains had been raised up, the cold climate being directly coin- 
cident with such elevations of vast masses of land and extensive sea-bottoms. 
Admitting for a moment the applicability of this theory of Mr. Croll, would 
not, 1 ask, the intervention of ice-action in warm, hmnid, and equable periods 
have left some traces in the natural-history products of such colder fits ? Ought 
we not to meet with some animals and plants indicative of such cold climates ? 
But as no signs of this sort have been detected in Palaeozoic rocks, I cannot 
admit that a few striated stones or erratic blocks detected at wide intervals only 
in some old conglomerates, can in fairness be adduced as indications of such 
grand and general changes of climate in those olden days, when the seas of our 
planet and its lands contained, as far as observation goes, no living thing which 
does not bespeak a moderate and moist if not a warm climate. 
On this point, indeed, my own view is supported by the opinion of Sir Charles 
