396 The American Naturalist. [M ay, 



attacks sulphides, but otherwise is of much value in separating mixt- 

 ures of heavy minerals. 



La Touche 10 describes an apparatus to be used in connection with 

 diffusive columns of methylene iodide for the purpose of determining 

 the density of minute fragments of minerals. 



GEOLOGY AND PALEONTOLOGY. 

 Geology of the French Congo.— The Congo region belonging 





I greater in extent than the parent country. 



enterprise of different explorers and the researches of scientific men, 

 notably geologists and paleontologists, much information concerning 

 this great tract of country has been acquired since 1871. M. Barrat 

 has systematized the facts on record and publishes an interesting paper 

 under the title " Geology of the French Congo," in which he embodies 

 also the results of his own explorations in the valley of the Ogoove. 



The observations of M. Pouel, made during a stay of many years in 

 the region under discussion, confirm the conclusions of M. Barrat as to 

 the great stratigraphic uniformity of the Congo. Furthermore, the 

 formation of the basin after the uplift of the African plateau is ex- 

 plained by the progressive draining of a series of reservoirs, more or 

 less depressed, placed at different altitudes and discharging from one 

 to another toward the ocean. The limits of t 



relation to the ancient rock ridges now hidden beneath the sandstone 

 but occasionally laid bare by erosion. 



Around the border of the basin, the formations plainly demonstrate 

 that they were elevated as early as the carboniferous epoch, and al- 

 though greatly leveled since, still show the primary reliefs. One of 

 the most interesting is the formation of Adamaona ; its substratum is 

 granitic and metamorphic like the Crystal Mountains and the Mou- 

 amba Mountains and the region of Katanga, and there are also rocks 

 which are similar to the Devonian of the Lower Congo. The whole 

 formation has been intersected and to a great extent covered by 

 erupted material, probably Cenozoic, and by outflows from volcanoes 

 of undoubtedly much more recent age. 



The structure of the plateaus of Adamaona is somewhat analogous 

 to that of the central plateau of France. (Extr. Ann. des Mines liv. 

 d'Aril, 1895.) 



