320 ANNUAL OF SCIENTIFIC DISCOVERY. 



account were taken of the altered form of the drops as they descend, but as 

 we are ignorant of the nature and amount of this change we can not deter- 

 mine its effect on the terminal velocity. 



If, instead of assuming the descending globule to consist of water through- 

 out its whole volume, we suppose it to be a hollow shell of water like a 

 microscopic soap-bubble, it is obvious that for the same diameter the terminal 

 velocity would be greatly less than in the above table. Admitting with 

 Saussure and others that clouds are made up of such hollow vesicles of ex- 

 treme minuteness, it can be shown that their descent to the earth would be 

 so slow as to make their gravitating tendency inappreciable during the short 

 time in which we watch them as they float by. 



OX THE EPOCH OF THE MAMMOTHS ; ELEPHAS PEIMIGENIUS. 



At a recent meeting of the Boston Society of Natural History, Professor H. 

 D. Rogers called attention to the interesting palasontological fact that while 

 the remains of the fossil elephant or Siberian mammoth of the Eastern Conti- 

 nent are imbedded in the great drift stratum, those of the fossil elephant of 

 America are as invariably above it, lying in superficial deposits of a distinctly 

 later age. It is now generally conceded that the relics of the Mastodon gi- 

 ganteus of North America, which do not extend beyond this continent, are 

 nowhere involved in the general or earlier drift, but lie upon it, inclosed either 

 in more recent swampy deposits, or in the nearly as recent later local diluvial 

 clays and gravels of the great lake and river valleys of the country. But the 

 fact that the bones and* teeth of the extinct elephant on this continent are en- 

 tombed in the same superficial materials seems not to have been sufficiently 

 adverted to by geologists, or, if passingly stated, its bearings have been over- 

 looked. 



That the American elephant was the cotemporary of the Mastodon giganteus 

 is not only proved by the occurrence of great numbers of their teeth and 

 bones side by side in the great marshy alluvium of Big Bone Lick, but is 

 manifest on a scrutiny of the conditions under which its remains are alleged 

 to be imbedded. A careful review of all the cases on record of the positions 

 of the elephant remains must satisfy geologists, familiar with the more recent 

 strata of this country, that these two colossal animals lived together in the 

 long period of surface tranquillity which succeeded the strewing of the general 

 drift (the period of the Laurentian clays), and were overtaken and extermin- 

 ated together by the same changes, partly of climate, partly of a second but 

 more local displacement of the waters that namely which reshifted the drift, 

 and formed our later lake and river terraces. The fact that these extinct 

 animals thus occur only above the true drift in North America, and in it in 

 Siberia and Europe, would seem to indicate one of two things: either that the 

 drifts of the two continents are not of the same epoch, or these being of one 

 age, that the fossil elephants of the two regions are not of one and the same 

 species. It' we admit, with the great body of geologists, that the general 

 drift-covering of all the northern latitudes of both continents is of one origin 

 and one date, we are constrained to regard the mammoth of these respective 



