Retiem — Hecr’s Primceval World of Switzerland. 79 
downwards, but have tumed upwards also. The dear old Stigmaria, 
without a Sigillaria stem, is growing in the water, as in the early days 
of geological inquiry. 
In Order to account for a Carboniferous fauna and flora in high 
northern latitudes, Dr. Heer advocates the theory that at that time 
the preponderant heat on the earth was not that of the sun. It is, 
however, a generally-received doctrine among geologists and physicists 
at the present day, that the influence of the earth’s internal heat had 
ceased to affect the climate of the globe long before either its crust, 
its waters, or its atmosphere had become sufficiently modified to 
admit of their becoming the abodes of living organisms. Any appeal, 
therefore, to the internal heat of the earth in explanation of abundant 
animal and plant life in high Arctie regions, either in Palteozoic or 
Neozoic times, must be deemed unsatisfactory at the present day ; and 
the key to the solution of the problem must be sought either in a 
change in the inclination of the earth’s axis, an increase of the sun’s 
heat, or probably in a combination of these causes together with a 
complete change in the relative distribution of land and sea in both 
hemispheres. Prof. Heer seems to regard the absence of light 
duriug the long Arctic winter as unimportant, provided the heat 
was only maintained well above freezing-point. Even the insects 
of the Coal Period he believes to have been chiefly nocturnal. But 
there were many diurnal insects present in the Coal Period besides 
the noctumal Termites and Cock-roaches. 1 
The accompanying figure is (together with others), by the courtesy 
of Hr. Hey wood, reproduced from Prof. Heer’s work. 
Fig. 1. Blatta Helvetica, Heer, Coal-measures, Erbignon. 
a. 'Wing of the natural size. b. The entire insect (restored by Heer). 
’ See Quart. Journ. Geol. Soc. 1876, vol. xxxii. pp. 60-64, pl. ix. ; and Geol. 
Mag. 1876, Decade II. Yol. III. pp. 519-520. 
