Aug. 10, 1888.J 



SCIENTIFIC NEWS. 



141 



light upon the eruptive periods of the past formation of 



1 our globe. 



Certain ancient crystalline rocks, common in the 



-, Pyrenees, were distinguished by the name of ophites. 

 Neither the date of their formation'nor their origin was 

 definitely determined, until in 1877 M. Levy proved 

 that they were eruptive, and that they displayed under 

 the microscope a peculiar structure which he designated 

 by the name of ophitic structure, in which the felspar 

 appeared united by very large tablets of augite. It thus 



" appears that these ophitic rocks are igneous rocks in 

 which the cooling down has proceeded much more 

 slowly than in the ordinary products of contemporary 

 eruptions. In endeavouring to reproduce the ophitic 

 type by synthesis, it is necessary to crystallise the augite 

 ■during a phase distinctly separated from that during 

 which the felspar is produced, and to give ample time 



k during the first period for the formation of the crystals 

 into large spaces. For this purpose, a mixture of 

 anorthite and augite was subjected, after fusion, to a pre- 

 liminary annealing, during which it was kept for four 

 days at the temperature of melting steel, when some 

 anorthite separated. A second annealing of equal 

 duration at the temperature of melting copper induced 

 the crystallisation of augite in large masses, which formed 

 a mould for the felspar, and attracted little octahedrons 

 of magnetite and picotite to it. The eruptive origin oi 

 ophites and the cause of the structure were thus incon- 

 testably established by this noteworthy synthesis. 



Thus we have convincing proofs of the service ren- 

 dered by synthesis in enlightening us as to the origin of 

 rocks, and in settling the discussions which, even in the 

 present day, still arise apropos of the principal cry- 

 stalline types of the modern epoch, as, for example, in the 

 case of the basalts, in which some scientists would fain 

 discover traces of aqueous agency, but in which, in com- 

 mon with all volcanic rocks of contemporary eruptions, 

 these experiments tend to prove a distinctly igneous 

 origin. 



But scientists have not always obtained these magni- 

 ficent successes ; many of their attempts have proved 

 utterly fruitless. It is advisable to recall these defects 

 ■occasionally, as they point out which paths must be 

 avoided if the final truth is to be reached. These 

 failures circumscribe the field of future experiments and 

 trace the limits within which hypotheses must be con- 

 fined. Moreover, they show that these rocks, whose 

 synthesis the methods employed have failed to gain, 

 must have been formed under conditions differing from 

 those by which actual volcanic products were produced. 

 This conclusion, to which former analyses and observa- 

 tions already pointed, without, however precise certainty 

 as to its causes, is amply confirmed by the failure of 

 the synthesis. If it has succeeded in satisfactorily 

 reproducing the lavas of modern volcanoes, it has 

 completely failed in the imitation of those whose forma- 

 tion no longer occurs in contemporary eruptions. 

 Broadly speaking, one may say that, up to the present, 

 all the acid rocks have evaded synthetic formation, as, for 

 example, all those which include, amongst their mineral 

 constituents, quartz, mica, orthose, or hornblende. The 

 processes of nature are not due to unknown forces ; per- 

 chance, therefore, by combining those over which we 

 already have control, by modifying their application we 

 might eventually succeed in reproducing those rocks 

 which up to the present have eluded our efforts, a hope 

 which we may surely found upon the results already 



obtained, since they may be but the precursors of still 

 more remarkable achievements. It is but a repetition 

 of the axiom that the defeats of the past prepare the 

 way for the victories of the future. We have endea- 

 voured, in this rapid review of the progress of litholo- 

 gical synthesis, to show the high scientific importance of 

 the researches instituted at the Geological Laboratory of 

 the College of France. We might have enumerated the 

 no less remarkable synthesis of minerals and meteorites, 

 conducted with such good results by other clever scien- 

 tists and their pupils, foremost amongst whom stands 

 M. Bourgeois, but space fails us. Still we have at least 

 sufficiently proved how much these methods have en- 

 larged our knowledge in a domain of nature where all 

 access once seemed denied to us. 



Hitherto, wherever the torch of experimental methods 

 has penetrated, it has fully and clearly illuminated the 

 most striking phenomena of the science of the earth. To 

 indicate the extent of the field of mineralogical science 

 already explored by experimental science, it is only 

 necessary to mention the name of Daubree, the direct 

 descendant of many illustrious geologists of the Scotch 

 school. By degrees the processes have been successfully 

 applied to the interpretation of metalliferous deposits, 

 of metamorphic rocks, of the phenomena of trituration, 

 and of the transportation of sedimentary matters, and 

 to the study of the fractures and distortions of the 

 earth's crust, of the schistosity of the rocks, and of 

 certain features of the structure of the mountains. 



Thus geology, after having passed through the succes- 

 sive phases of observation and analysis, has entered into 

 the phase of experiments and synthesis, which endeavours 

 to imitate the powerful creations of nature, thus crown- 

 ing the scientific edifice by processes which facilitate the 

 discovery of the several causes whose complete com- 

 prehension is the final aim of physical and natural 

 science. It is this crowning triumph which Leibnitz 

 presaged two centuries ago, when he wrote : — " He who 

 succeeds in carefully comparing the products drawn from 

 the depths of the earth with those of the laboratories, 

 will accomplish a great work, for then at last we shall 

 clearly see the striking similitude which exists between 

 the products of nature and of art. Although the in- 

 exhaustible Creator has innumerable methods of carrying 

 out His wishes, yet there is always a certain consistency 

 even in the variety of His works. It is already a great 

 step towards the perfect knowledge of causes and effects 

 to have discovered a means of producing them, for nature 

 is but art in magnified proportions." 



CORRESPONDENCE. 



The Editor does not hold himself responsible for opinions expressed 

 by his correspondents, nor can he take notice of anonymous com- 

 munications. All letters must be accompanied by the name and 

 address of the writer, not necessarily for publication, but as a 

 guarantee of good faith. 



WEATHER OF JULY, 1888. 



In reference to St. Swithin and his mission this year, dis- 

 appointment is expressed that the subject has not received 

 as much attention from the weather-prophets as is usual at 

 this time. 



They have probably been content that the public are fully 

 aware of the old proverb, which again has proved substan- 

 tiated, and that it is known to be not an uncommon thing for 

 July to be wet, as in 1879-80. 



A collection of rainfall observations at sea in course of for- 

 mation, and so far summarized, leads one to infer that our 



