674 Chronicles of Science. [Oct., 



VI. GEOLOGY AND PALAEONTOLOGY. 



(Including the Proceedings of the Geological Society.) 



Geology is now so comprehensive a science, the number of labourers in 

 its many fields has become so great, their discoveries are so numerous, 

 and the advance of the science is so rapid, that in the few pages devoted 

 to this Chronicle we can only pretend to give outlines of some of the 

 most important subjects occupying the attention of geologists, together 

 with notices of a few of the best investigations into the structure of 

 our own islands. Frequently we are obliged to omit all mention of 

 valuable results arrived at, both at home and abroad ; and our endeavour 

 has generally been to give as complete notices as possible of a few of 

 the most instructive and successful researches that have recently been 

 carried out, rather than short accounts of everything that has been 

 published during each quarter, as in the latter case our Chronicles 

 would have been little better than booksellers' catalogues. We have 

 also endeavoured to select our subjects so as to show that important 

 advances are continually being made in our knowledge of the structure 

 of the earth, and of the forces which have modified its surface in past 

 times ; and it is with this view that we have sometimes given great 

 prominence to apparently " out of the way " researches. 



"Within the last two or three years much attention has been given 

 to the Physical Geography and Geology of the Sahara ; and attempts 

 have several times been made to explain important phenomena by 

 means of the ancient condition of that vast and sterile area. The last 

 two numbers of this Journal have contained communications relating 

 to one supposed effect of the Sahara on the Meteorology of the globe, 

 and our readers will therefore feel some little interest in the other 

 phenomena which have been thought to have more or less connection 

 with either its past or present condition. 



The present characters of the Sahara are too well known to need 

 description at our hands ; but, considering them geologically, the 

 question inevitably arises, When did the Sahara first assume these 

 features ? It appears that the great geographer Ritter, nearly half a 

 century ago, suggested " that the African desert had been under water 

 at a very modern period ;"* and in 1852, M. Escher von der Linth 

 gave it as his opinion, " that if this submergence were true, it would 

 explain why the Alpine glaciers had attained in the Post-pliocene 

 period those colossal dimensions which Venetz and Charpentier, rea- 

 soning on geological data, first assigned to them."f The subsequent 

 discovery of the common existing cockle and other marine shells in 

 the heart of the desert, and at various depths beneath the surface, left 

 no doubt as to the submergence ; and, granting this, M. Escher's con- 

 clusion seems reasonable enough, for everybody knows how the sirocco 

 (called Eohn in Switzerland) sometimes nearly strips the Alps of their 

 snowy covering. Sir Charles Lyell has also remarked, that during 

 the submergence of the Sahara the sirocco would not only be deprived 



* Lyell's ' Elements,' sixth edition, p. 175. f Op. et loc. cit, 



