CORRESPONDENCE. 



295 



Pig. 16, 17. Erondicxjlaria Archiaciaka, D'OrUgny. 



A narrow form of F. complanata, Defrance, of which there is an endless series of 

 modifications. These are really chevron-chambered NodosariEe. Frondicularise 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. Fig. 17 is an 

 edge-view. 



Fig. 18, 19. Yagintjlina costulata, Reuss. 



A variable Nodosariau form, abundant in the Gault and Chalk-marl ; rare 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. 



Pig. 20, 21, 22. Prokdicularia Cordai, Beuss. 



Frondicularise, or flattened, chevron-celled 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. "When 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'Orbigny's Flabellina rugosa ; indeed Fig. 22 

 shows a little eccentricity of the first chamber. Frondicularia is to Flabellina as Nodo- 

 saria is to Marginulina and Vagulina. Fig. 21 is an edge- view. 



Pig. 23, 24. Deisttalina gracilis, D'Orhigng. 



A variety of the world-wide B. communis, D'Orbigny, which occurs in all geological 

 formations from the Palaeozoic upwards. D. communis itself 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. 



COREESPONDENCE. 



Causes of Cosmical Changes of Temperature on our Planet. 



That the vine, the walnut, the plane-tree, etc. etc., once nourished within 

 the Arctic Circle, and that Mount Lebanon was for a long period covered 

 with ice and snow, are facts inexplicable by 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, which 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 changes 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 beiug a negation of everything that is 



