358 POPULAR SCIENCE MONTHLY. 



examine, and which have been formed in his investigations of 

 the perforation of rocks by gaseous explosions. In these experi- 

 ments, channels were opened through the granite by the gases of 

 nitroglycerin, showing on their vitrified surfaces all the stages, 

 from the drawing out of a thin pellicle of melted glass to the for- 

 mation of a perfect spherule. Grains of two different categories 

 may be distinguished with the microscope in the dusts produced 

 in the trituration of rocks by the violent passage of gaseous ex- 

 plosions. Some can not be distinguished from those produced by 

 simple mechanical pulverization. But, besides these materials 

 angular grains of quartz, feldspar, and mica we find abundance 

 of perfect, or nearly perfect, spheres, opaque and black or slightly 

 translucent and brownish, with shining surface and often the 

 characteristic little neck. Identical elements are found in the 

 dust derived from different rocks that have been submitted to ex- 

 periment, but with features that vary in each of them. 



Dust obtained from the lava of Vesuvius exhibits the globuli- 

 form character in the highest degree. Nearly all the matter is in 

 the condition of black globules of various dimensions, but always 

 very light, and sometimes having a tubulure. The abundance of 

 these globules is manifestly associated with the relatively easy 

 fusibility of the rock, which is also represented in the constitution 

 of the general glaze with which all the parts that have been in 

 contact with the incandescent gases are covered. The identity of 

 these globules with those that exist so abundantly in the atmos- 

 pheric dusts- and marine sediments can not be contested. Till 

 now, says M. Daubrde,* the general opinion, and the only one pos- 

 sible, has been to connect the origin of these globules with the ar- 

 rival of cosmic masses in the atmosphere ; and we may add now to 

 the arguments already presented in support of this thesis, the re- 

 sults afforded by the gaseous trituration of meteoric rocks. The 

 dust furnished by a stone cylinder that fell from the sky in 1888, 

 at Pultusk, was marked by innumerable globules, associated with 

 fragments of peridote and entastite, and with metallic granules 

 which had preserved their ramified form and their adherence to 

 lithoid minerals. What we have said shows also that terrestrial 

 rocks, as well as meteorites, may engender these globules. Hence 

 the arrival of meteorites into the atmosphere incontestably con- 

 tributes greatly to the production of the brilliant globules so 

 abundant in ae'rian and aqueous sediments. It seems also to be 

 established that the openings of diatremes \ have an active part in 



* Lea Regions invisibles du Globe et des Espaces celestes (The Invisible Regions of the 

 Globe and of Celestial Space). Paris, 1892. 



f Cylindroid vertical apertures traversing the crust of the earth, of which the diamond- 

 bearing pans of the Cape and volcanic chimneys furnish well-known types. 



