COEBESPONDENCE. 
295 
Fig. 16, 1.7. Frondicularia Archiaciai^a, D'OrUgny. 
A narrow form of F. complanata, Defrance, of which there is an endless series of 
modifications. These are really chevron-chambered Nodosarise. Frondiciilarise are 
common in the Gault, Chalk-marl, and Chalk, and occasionally are found abundant in the 
Tertiary beds, and are not wanting in some parts of the existing seas. Eig. 1? is an 
edge-view. 
Fig. 18, 19. Yagintjlina costulata, Reuss. 
A variable Nodosarian form, abundant in the Gault and Chalk-marl ; i*are or wanting 
in the Chalk. Fig. 18 is a view of the edge, which is as variable in thickness as the 
shell is in its other measurements. 
Fig. 20, 21, 22. Frondicxilaria Cordai, Beuss. 
Frondicularise, or flattened, chevron-ceUed Nodosarise, vary continually as to the 
length of the backward elongations of the cells, as the two figured specimens (from the 
Chalk-marl or the Gault) here show. ^Vhen they commence with a spiral arrangement 
of the cells, they are known as Flabellinfe ; and excepting in this point, there is little 
or no distinction between Fig. 20 and D'Orbiguy's FlaheUhm rugosa ; indeed Fig. 22 
shows a little eccentricity of the first chamber. Frondicnlaria is to Flabellina as Nodo- 
saria is to Marginulina and Vagulina. Fig. 21 is an edge- view. 
Fig. 23, 24. Dentalina gracilis, D'OrUgny. 
A variety of the world-wide D. commimis, D'Orbigny, which occurs in all geological 
formations from the Palaeozoic upwards. I), communis itseU is a feeble form of Nodosaria 
Raphanus. Fig. 23 is the end-view, showing the aperture. 
In the above remarks I have incorporated much information derived from my friend 
Mr. W. K. Parker. 
COERESPONDENCE. 
Causes of Cosmical Changes of Temperature on our Planet. 
That the vine, the walnut, the plane-tree, etc. etc., once flourished within 
the Arctic Circle, and that Mount Lebanon was for a long period covered 
with ice and snow, are facts inexplicable b)'' any meteorological causes now 
in action, every geologist of the present day I believe admits. The ques- 
tion is to what causes, not now meteorologically evident, are we to attri- 
bute the great changes of temperature on our planet, wliich have extended 
over such long periods as those recorded by the unquestionable and well- 
established testimony of glaciation. Must we carry our solar system into 
remote regions of space in order that we may theorize on cosmic changes 
of temperature, or can we explain" these truly wonderful facts by some 
changes in our own planetary motions, such as our earth getting into a zone 
of asteroids, to clianges in the sun's atmosphere, either as to surface or 
intensity, as already published by Mr. Mackie, in a former number of the 
' Geologist ' ? With regard to the theory of the earth passing through hot 
and cold regions of space, Mr. Mackie asks, " If heat be confined to mat- 
ter, how can we speak of hot and cold regions of space, where by that very 
admission neither heat nor cold can be ? " The reply to this question is 
not difficult. Matter cannot exist without space, but space can exist with- 
out matter. By hot and cold regions of space, I could only mean those 
portions of space occupied by matter, for where there is no matter there 
could be no temperature, neither hot nor cold as sensations, nor caloric as 
a material condition ; for whether heat be a fluid or a wave, it can have no 
existence in pure space, pure space being a negation of everything that is 
