260 
POPULAR SCIENCE REVIEW. 
Slickensides in the Granite near Dublin. — In a paper read during the 
summer before the Geological Society of Dublin, it was pointed out by the 
Rev. Maxwell Close, that our notions of the phenomena productive of 
these striations are exceedingly unsatisfactory. In Dublin granite, a 
great number of surfaces (which, in the author’s opinion, are always joint 
surfaces), and which present more or less marked striations, may be ob- 
served. Some of them are indicated in the maps of the Geological Survey, 
and all of them are like the peculiar groovings known as galena sliclcen- 
sides. Indeed, the resemblance to the latter is so great, that Mr. Close 
concludes that a cast of one could not be distinguished from a cast of the 
other. After enumerating the existing theories, none of which sufficiently 
account for the phenomena referred to, the author advances a new hypo- 
thesis — that of crystallization. Several facts are brought forward in 
support of this view, and the paper concludes with the following remarks : 
“ The striated coatings are later than the joints which carry them : they 
were formed after the consolidation of the granite, but also they were 
formed before certain other joints which cut through them, or before the 
granite had attained its final structural condition ; that is to say, after the 
cooling of the granite had begun, and before it was completed. Perhaps 
we may have in thermo-electric currents the polarizing force we seek. 
We know that light is able to influence crystallization, as also the action 
of a powerful magnet. It seems easier to explain by thermo-electric 
agency than by the more widely acting currents of terrestrial magnetism, 
the variation in direction of the striations which we have noticed, and also 
the fact that near the boundary of the granite (when the cooling of the 
intruded mass must have been comparatively rapid and irregular), the 
slickenside phenomena are either absent or confused .” 
The Earth's Crust. — A paper of a peculiarly speculative type was 
recently read on this subject before the Natural History Society of Mon- 
treal. The writer endeavoured to work out the theory supported by Sir 
H. de la Beche, of the incandescent character of the globe, prior to the 
development of organic beings. The paper is one of considerable length, 
and bears evidence of the author’s having given the question serious 
consideration. As prefatory to his argument, the writer (Mr. Macfarlane) 
states : — 6i It is, I believe, possible to maintain, with every appearance of 
reason, that the primitive gneiss formation constitutes the first solidified 
crust of the originally fused globe, and that the crystalline and sub- 
crystalline rocks of the primitive slate formation are the products of a 
peculiar transition period, during which aqueous fluids gradually accu- 
mulated on the surface, and the latter attained a temperature approaching 
somewhat to that of the present day.” 
The Sternum of a Fossil Tortoise from the Gypsum Hills of Sannois is 
described by M. Valenciennes, in a memoir presented to the French 
Academy on the 23rd of November last. The peculiarity of the observa- 
tions is that the latter are made upon an animal which has not been 
found complete, but which has been reconstructed. “ Birds,” says the 
distinguished naturalist who contributed the memoir, e< have the sternum 
composed of five pieces ; tortoises invariably possess nine sternal portions. 
This number once determined, led me to believe that this was a case in 
