548                                                 SILURIA.

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 you have placed in my hands, is a Foraminiferal
organism."

Dr. Carpenter has also carefully examined a portion of the specimen figured
in Plate XLI. fig. 32 (named ' Stromatopora nummulitisimilis' in the Sil. Syst.),
and he corroborates the statement given in the last edition as to its oolitic
nature 5 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 orsranisms.
 

S.—A New Theory of several former Glacicd Periods (p. 505).

In the concluding pages of this work a brief allusion only has been made to
what I term the gTeat 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 fiourished, and when, according to certain writers, man him¬
self existed. Recently, however, this theory, founded on the changes in the
obliquity of the ecliptic, has been ingeniously extended by Mr. (ilroll 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 aUowed, his theory may be applied during aU geological
periods.

Now this \dew 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 dimng the Silurian epoch, and the similarly
broad extension of the same land-plants in the Devonian and Carboniferous
epochs, are aU 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 learn 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. CroU, would
not, 1 ask, the intervention of ice-action in warm, humid, and equable periods
have left some traces in the natural-history products of such colder fits P Ought
we not to meet with some animals and plants indicative of such cold climates P
But as no signs of this sort have been detected in Palaeozoic rocks, I cannot
adnut 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