340 CLIMATIC CONDITIONS OF THE GLACIAL EPOCH. 



■where it has been demonstrated ; and tlie cause of tliis retreat, if we succeed 

 in ascertaining it, will be an important factor among those which engage our 

 attention in the stndy of the physics of the globe."* 



The results at which we seem to have arrived in connection with the 

 question with which we have been occupied in the present section may be 

 summed up as follows : In all the mountain chains upon which glaciers are 

 developed, and which have been accurately mapped and are at the same 

 time sufficiently accessible to scientific observers, or which are constantly 

 being visited by tourists and their guides, there has been observed a general 

 diminution in the size of the ice streams, so marked as to excite universal 

 attention. This shrinkage has been going on for from twenty-five to fifty 

 years, with slight oscillations, and with an apparent genei'al increase rather 

 than diminution of rate. It has progressed to such an extent that the prin- 

 cipal glaciers of the Mont Blanc district are several thousand feet shorter 

 than they were forty or fifty years ago. When we seek to ascertain Avhether 

 a corresponding recession has been taking place in other less accessible 

 chains, and especially in the Himalaya and the Scandinavian Range, we 

 meet with considerable difficulty, because although the fact of a shrinkage 

 is clearly indicated, we are unable, from want of accurate and continuous 

 observations, to say how much of this has taken place within a few years, 

 and thus belongs to the present phase of glaciation in the Alps, Pyrenees, 

 and Caucasus, and how much of it might be referred to a prehistoric period 

 of recession, and thus be connected Avith the Glacial epoch, representing in 

 point of fact, according to the popularly received theory, a phase of geo- 

 logical history which began and ended long agQ, and not one belonging to 

 the present epoch. 



When we examine the records of meteorological observations taken in 

 the Alps during the past fifty years, using only such as can be depended on 

 for accuracy, we find no light thrown on the causes of this recession. That 

 is to say, we have, on the one hand, an apparently pretty constant diminu- 

 tion of the ice masses from the Mediterranean Sea to the Caspian ; and, on 

 the other, numerous irregular oscillations of temperature and rain-fall, but 

 no perceptible permanent change, and none in any constant direction during 

 the half-century over which the observations extend. It is true that we have 

 not the means of comparing the average of the fifty years ending with 1875 



* r.iiUetin rle la Smricte Vamloise des Sciences Naturelles (2), XVII. pp. 422-425. Translatinn in Popular 

 Science Review, New Series. Vol. V. p. 319. 



