Maech 1, 1907] 



SCIENCE 



351 



perature prevailing even in late preglacial 

 times all over tlie globe, that we instinctively 

 seek for some more cogent cause of the wide- 

 spread glacial phenomena that followed so 

 closely upon the periods of greatest mountain- 

 making recorded in geological history. 



It is not the purpose of this paper to dis- 

 cuss the glacial theories alluded to above in 

 detail, that having been done by many able 

 writers; but rather to call pointed attention 

 to another hypothesis now before the scientific 

 world for a number of years, and which seems 

 to me to offer a complete solution of the prob- 

 lem, provided it can pass the criticism of 

 physicists; for from the geological point of 

 view it seems to suffer no valid^ objections. 



' While it is evident that extended glaciation 

 existed in the Permian era, the claim that it was 

 as extensive and continuous as the Pleistocene 

 glaciation does not seem to me to be well estab- 

 lished. The Permian having been, as is strongly 

 emphasized in Chamberlin and Salisbury's ' Hand- 

 book of Geology,' a time of extended deformation 

 of the earth's crust, to which the deflection of 

 ocean currents, causing glacial conditions, is 

 ascribed by them, it seems quite reasonable to 

 suppose that such deformations extended to the 

 upraising of large areas, together with erogenic 

 uplifts, of which no evidence now remains except 

 the seaward borders of the glaciated areas, with 

 their till and roches moutonnfees, such as we now 

 see at the foot of glaciers. It is pertinent to in- 

 quire, in this connection, by what imaginable 

 changes in land areas and ocean currents the 

 north and south polar regions could at this time 

 remain deglaciated and made to grow magnolias, 

 figs and the like. The Arctic Ocean is now sub- 

 stantially closed to equatorial currents; the Ant- 

 arctic is wide open; yet both are glaciated. What 

 intermediate arrangement could give either or 

 both a temperate climate, with or without more, 

 or less, carbon dioxid? 



The claim that aridity is shown by the preva- 

 lence of evaporation-deposits of rock-salt andi 

 gypsum, is hardly tenable alongside of that made 

 for glaciation. The low temperature and abun- 

 dant moisture required for glaciation do not seem 

 compatible with arid heat. Evaporation due to 

 currents of undersaturated air, such as always 

 characterizes descending air currents, is very 

 effective; and the arid conditions would hardly be 

 expected to extend as far north as Stassfurt. 



This hypothesis or theory (for it seems rather 

 to deserve the latter nam.e from its comprehen- 

 siveness) first brought forward by Dr. Mars- 

 den Hanson in 1891, has until lately suffered 

 the initial fate of many others now generally 

 accepted, viz., that of being ' todtgeschwiegen ' 

 at first, as being too much opposed to some 

 generally accepted, but by no means proved 

 dicta regarding earth-heat, and especially the 

 time-limit of its influence upon terrestrial 

 surface-temperatures. Physicists at one time 

 claimed that the globe as a whole is more 

 rigid than steel, since it must otherwise suffer 

 sensible tidal deformation; but were met by 

 the ocular proof, known to every geologist, 

 that so far from being even moderately rigid, 

 the crust as known to us is a mere congeries 

 of fragments in unstable equilibrium and in 

 more or less constant movement for readjust- 

 ment.' We are now told that the transmission 

 of earth-heat to the surface must have ceased 

 in early geological time, because of the low 

 conductivity of the rocks known to us. But 

 the enormous effusions of molten rock even in 

 late Tertiary times, followed by manifestations 

 of vulcanism which, though now apparently in. 

 course of extinction, proves the continued ex- 

 istence of high temperatures not far below the 

 surface crust, again invalidates the physicists' 

 objection, because based on the arbitrary as- 

 sumption that conduction was the main or 

 only manner in which the interior heat could 

 reach the surface. 



It is evident that whatever may have been 

 the original source of that heat, whether from 

 cosmic contraction or planetesimal collision, 

 it has existed and exists now, even though 

 practically insensible at the earth's surface. 

 Even if, as some believe, to-day's vulcanism 

 were only ' skin-deep,' the evidence of former 

 much greater heat is too strong to be set aside. 

 That this heat must have been brought up from 

 the depths of the earth-mass by water, aqueous 

 vapor and other gases, as is now the case in 

 volcanic eruptions, and is also being done by 



' See, for the latest discussion of this subject, 

 the paper on ' The Geodetic Evidence of Isostasy,' 

 etc., read before the Washington Academy of Sci- 

 ences by John F. Hayford, May 18, 1906. 



