126 



SCIENTIFIC NEWS. 



[Aug. io, i J 



necessary for this experiment. Half fill one with water 

 and the other with strong brine. Into the water drop an 

 egg. It goes to the bottom (fig. 7). An egg dropped 

 into the brine floats (fig. 8). By carefully pouring the 

 brine through a long funnel or through a funnel with an 

 attached tube, which will reach to the bottom of the 

 tumbler containing the pure water, the water and the 

 egg will be lifted, and the egg will float in equilibrium at 

 the middle of the tumbler. The first experiment shows 

 that the egg is a little more dense than pure water, the 

 second that brine is more dense than the egg, and the third 

 that the egg can be supported in equilibrium between 

 two liquids of different densities. — Scientific American. 



THE GLACIAL EPOCH AND THE 

 PRESENT DAY. 



A LTHOUGH the former existence of a glacial epoch 

 ■'*■ has passed out of the region of discussion, there are 

 still unsolved questions concerning its origin, its 

 character as single or recurrent, and the possibility of its 

 return. The absolute decision of some of these problems 

 is not to be hoped for to-day or to-morrow. In the 

 meantime every light procurable, be it direct or indirect, 

 is highly welcome. Professor Bruckner, in discussing 

 some of these points in Humboldt, observes that 

 though the geologist is not in a position to apply any 

 absolute standard of time in measuring the history of the 

 earth he may, by a cautious and critical evaluation of the 

 effects of certain forces, form an estimate of the relative 

 duration of certain geological epochs. 



The most recent geological time, the diluvial epoch, 

 is characterised by an enormous development of glaciers. 

 From the Scandinavian Mountains they passed south- 

 wards to the foot of the central mountains of Germany 

 and into the heart of European Russia. The Baltic had 

 no existence as a sheet of water, its bed being choked 

 with ice-masses. The glaciers of the Alps filled not 

 merely the mountain valleys, but spread over the sub- 

 alpine territories, both northwards and southwards. A 

 corresponding development cf glaciation during the 

 diluvial epoch can be traced in North and South America, 

 in Asia, and Australia. Even within the Tropics our earth 

 did not escape the formation of glaciers, as their traces 

 have been lately recognised in the Sierra de Santa Marta, 

 in South America. 



A careful examination of the diluvium leads, in many 

 localities, to the conclusion that the assumption of a 

 single glaciation does not suffice for the explanation of 

 the deposits. There were recognised two glaciations, 

 two icy periods, separated by a milder inter-glacial age. 

 Penck, on examining the region between the Iller and 

 the Inn, was led to the result that there must have 

 occurred a threefold repetition of glaciation, and Professor 

 Bruckner, on examining the Salzach region, confirms 

 his inference. Hence we find the following succession 

 of events : First glacial epoch forming glacier deposits, and 

 the oldest " schotter " of the glacier-streams (Bruckner 

 applies the term "schotter" to the gravel and other 

 debris with which streams originating in glaciers are 

 overloaded, and which they deposit in their beds). 

 First interglacial epoch, erosions by flowing water. 

 Second glacial epoch, repeating the phenomena of the 

 first. Second inter-glacial epoch, with repeated erosion 

 and deposition of the "loess" on the surface of the 

 ground. Third ice-age, with formation of the most 

 recent glacier deposits and stream " schotters." Then 



follows the post-glacial age, or alluvium, marked by 

 erosion due to flowing water. 



From these successive phenomena it is possible to 

 form an approximate conclusion as to the length of the 

 post-glacial age and its proportion to the time elapsed 

 between the third and the second ice-age. 



The three " schotter " systems have been piled up by 

 glacier-streams. Upon each period of accumulation 

 there followed a period of erosion which came to an end 

 when the next more recent " schotter " began to be 

 formed. To this alternating accumulation and erosion 

 is due the terrace, or stair-like structure of the three 

 " schotters." 



If we compare the destruction which the second 

 " schotter " underwent by erosion before the depositing 

 of the most recent " schotter " with the effects of post- 

 glacial erosion upon the latter, we recognise a noteworthy 

 difference. The erosive work of the post-glacial age (in 

 which we now live) is evidently small in comparison with 

 the erosive work of the second inter-glacial age. Hence it 

 seems that the time which has elapsed since the forma- 

 tion of the most recent " schotter " is shorter than the 

 time which intervened between the formation of the 

 second and of the third, or most recent " schotter." A 

 similar conclusion as to the duration of the first erosion- 

 period may be drawn from the great destruction of the 

 earliest " schotter " effected before the second was 

 deposited. We are in our day probably nearer to the age 

 of formation of the most recent " schotter " than it was 

 to the formation of the intermediate, or than this, again, 

 was to the first. The post-glacial age is decidedly shorter, 

 so far, than cither of the two inter -glacial periods. 



This conclusion drawn from the erosive actions in 

 the times concerned is confirmed by a comparison of the 

 layers of soil, deposited during the post-glacial age r.nd 

 during the inter-glacial age. We see the deposits of 

 the last ice-age covered only by a stratum of brown 

 clay, rarely exceeding a foot in thickness. But to the 

 inter-glacial period belongs the deposition of the strong 

 yellow strata of loess and loess-clay, and though the inter- 

 glacial character of these deposits is still in part con- 

 tested, yet the affirmative evidence is constantly 

 on the increase. A loess like that formed, accord- 

 ing to Professor Bruckner's observations, in the 

 second inter-glacial period and completed at its close, is 

 still wanting among the most recent diluvial deposits. 



The results thus described are rendered more impor- 

 tant by the consideration that they apply to the entire 

 northern sub-alpine country from Switzerland in the 

 west to Enns in the east. Hence the alluvial age is 

 merely the last phase of the diluvial epoch. 



That these results throw a certain side-light upon the 

 question of a return of the ice-age can scarcely be denied. 

 As the post-glacial age appears so decidedly shorter than 

 either of the inter-glacial ages, a recurrence of glaciation 

 appears in no wise excluded. But the question can be 

 definitely solved only when the causes of those climatic 

 changes which manifested themselves in the alternation of 

 glacial and inter-glacial epochs shall have been ascer- 

 tained, and their periodicity accurately determined for 

 the future. No geological evidence speaks against such 

 a recurrence ; but if we assume its return, we must 

 expect also a repetition of the " loess " period which 

 would precede the returning ice-age. However, the 

 next attack of glaciation, if it, is to be expected at all, 

 belongs to a future which in pur way of reckoning must 

 seem infinitely remote, 



