344 THE POPULAR SCIENCE MONTHLY. 



In the remarkable memoir on the phosphorites of Quercy, to 

 which I have referred, M. Filhol describes no fewer than seventeen 

 varieties of the genus Cynodlctis which fill up all the interval between 

 the viverine animals and the bear-like dog Amphicyon nor do I know 

 any solid ground of objection to the supposition that in this Cyno- 

 dictis- Amphicyon group we have the stock whence all the Viveridae, 

 Felidae, Hyaenidae, Canidae, and perhaps the Procyonida? and Ursidae, 

 of the present fauna have been evolved. On the contrary, there is a 

 great deal to be said in its favor. 



In the course of summing up his results, M. Filhol observes : 



" During the epoch of the phosphorites, great changes took place 

 in animal forms, and almost the same types as those which now exist 

 became defined from one another. 



" Under the influence of natural conditions of which we have no 

 exact knowledge, though traces of them are discoverable, species have 

 been modified in a thousand ways : races have arisen which, becoming 

 fixed, have thus produced a corresponding number of secondary species." 



In 1859, language of which this is an unintentional paraphrase, 

 occurring in the " Origin of Species," was scouted as wild speculation ; 

 at present, it is a sober statement of the conclusions to which an acute 

 and critically-minded investigator is led by large and patient study 

 of the facts of paleontology. I venture to repeat what I have said 

 before, that, so far as the animal world is concerned, evolution is no 

 longer a speculation, but a statement of historical fact. It takes its 

 place alongside of those accepted truths which must be taken into 

 account by philosophers of all schools. 



Thus when, on the first day of October next, the "Origin of 

 Species " comes of age, the promise of its youth will be amply ful- 

 filled ; and we shall be prepared to congratulate the venerated author 

 of the book, not only that the greatness of his achievement and its 

 enduring influence upon the progress of knowledge have won him a 

 place beside our Harvey ; but, still more, that, like Harvey, he has 

 lived long enough to outlast detraction and opposition, and to see the 

 stone that the builders rejected become the head-stone of the corner. 

 Nature. 



ATMOSPHERIC DUST * 



By GASTON TISSANDIER. 



EVERY one is aware that the atmosphere holds quantities of dust 

 in suspension. The dust betrays its presence by settling upon 

 our clothes, furniture, and other objects, but, on account of the minute- 

 ness of its particles, it can not be seen as it floats in the air, except under 



* Translated and abridged from the " Revue Scientifique." 



