P OP ULAR MIS CELL AX Y. 



689 



uppermost strata furnished by their decom- 

 position the carbonaceous material in the 

 associated rocks, the heat derived from the 

 slowly-cooling injected roclcs playing an im- 

 portant part in this process. Similar de- 

 posits of carbonaceous mineral in igneous 

 rocks are found in other localities, as at 

 Cape Gaspe, and in the lava of Mount Etna, 

 though in these cases it occurs in the less 

 concentrated form of mineral oil. But Mr. 

 Russell sees in these different forces only 

 different stages of one and the same pro- 

 cess. " If," he writes, " the cavities of a 

 rock were filled with petroleum by infiltra- 

 tion, and evaporation slowly removed the 

 more volatile portions, and oxidation took 

 place to some extent, the result would be 

 the formation of a deposit of soUd hydro- 

 carbon in the cavities. A similar process 

 sometimes occurs with bottled samples of 

 petroleum, by which the interior of the 

 bottle is left coated with a solid carbonace- 

 ous layer. In the rocks, if a fresh supply 

 of oil were furnished from time to time by 

 infiltration, the cavities would eventually 

 become completely filled with the solid car- 

 bonaceous residue. A vesicular lava might 

 in this manner be changed to an amygda- 

 loid, the cavities of which would be filled 

 with solid hydrocarbons instead of quartz, 

 zeolites, etc. Such, it appears to us, must 

 have been the history of the Triassic amyg- 

 daloid we have described, the cavities of 

 which must at one time have been filled 

 with mineral oil. This is but an epitome 

 of what took place on a grand scale at the 

 great fissure, over 1,400 feet deep, in New 

 Brunswick, which was filled with albertite, 

 and in the case of the Grahamite in West 

 Virginia, which also occupies an immense 

 fissure." 



Whence came the irctic Mammoth? — 



Were the mammoths whose remains are 

 found in the north of Siberia native in 

 that region, or were they carried thither by 

 rivers from a more genial climate ? If the 

 latter supposition were correct, we should 

 find the remains only in the vicinity of the 

 great watercourses, while, in fact, they oc- 

 cur in localities distant from the beds of 

 streams. But here fresh difiiculties face us, 

 for, though the mammoth was covered with 

 a thick coat of long hair, how could it live 



in a region where the temperature in Janu- 

 uary is as low as 65° Fahr., where the sum- 

 mer lasts only three or four months, and 

 where the vegetation is exceedingly scanty ? 

 The supposition is plainly inadmissible, and 

 hence either we must believe these remains 

 to have been transported hither, or else that 

 in early times the climate of Siberia was 

 much less severe than it is at present. Nor 

 is this a baseless theory, for, as Mr. U. H. 

 Howorth observes, the plants found in the 

 fissures of the rhinoceros-teeth (contempo- 

 rary with the mammoth) are those which 

 now live in southern Siberia. The plant-re- 

 mains associated with the mammoth (not 

 floated from a distance, but of the locality) 

 show the same thing, the species being 

 larch, birch, and other trees of good size. 

 Other evidences of the existence of a higher 

 mean temperature in Siberia at the time of 

 the mammoth are found in the fresh-water 

 and land shells associated with the remains, 

 but now extinct in northern Sibei-ia. As for 

 the manner of the mammoth's extinction, Mr. 

 Howorth beheves it to have been sudden. 

 The remains must have been preserved soon 

 after death. They were destroyed by a 

 flood due to some sudden convulsion, which 

 also changed the climate. 



Civilization and Teeth.— From the study 

 of 1,249 skulls, of which 844 represent 

 modern highly civilized races, and 277 mod- 

 ern inferior races, while the remaining 128 

 belonged to Romans, Etruscans, Phoeni- 

 cians, and other nations of antiquity, Pro- 

 fessor Mantegazza reaches conclusions which 

 go to confirm a remark made by Mr. Dar- 

 win in "The Descent of Man." "It ap- 

 pears," writes Darwin, "as if the posterior 

 molar or wisdom teeth were tending to be- 

 come rudimentary in the more civilized races 

 of man." Professor Mantegazza finds that 

 the wisdom-teeth are more frequently absent 

 in the superior than in the inferior types, 

 the exact proportion being 42-42 per cent, 

 in skulls of the higher races against 19'86 

 in the lower. But atrophy of the third 

 molar tooth occurs less frequently in the 

 higher than in the lower races, viz., in 10*90 

 per cent, of the former, and in 20-58 per 

 cent, of the latter. In the lower races the 

 abnormal cases are practically equal to the 

 normal, while in the higher they are much 



