1862.] 47 



have been frequently described, and the author confines himself 

 chiefly to pointing out the difference between them and the high- 

 level gravels. The climate at the one period has been described as 

 one of considerable severity ; but there is evidence to show that in 

 some part of the pliocene period, previous to that time, the cold 

 was still more severe. At the period referred to the greater part of 

 England was under the sea, whereas Switzerland and the greater 

 part of France had emerged at an earlier or a miocene period, and 

 there is no sufficient proof of their having been subsequently sub- 

 merged. This was the period of the wonderful extension of the old 

 European glaciers, which descended in the Swiss Alps, the Jura, 

 and the Vosges to within 1200 or 1000 feet of the sea-level, the 

 existing glaciers standing at 3400 to 3500 feet. M. Leblanc has cal- 

 culated that such a difference of level might be accounted for by a 

 reduction in the mean annual temperature of 12J Fahr. ; but the 

 author questions this, as the gradients of the glacier beds were much 

 less after they had emerged from the mountain-passes. The growth 

 of the old glaciers is rather the result of the great cold than a mea- 

 sure of it. Still it can be conceived that their growth would be 

 checked when the temperature had risen from the extreme cold to a 

 point 12| below the present mean annual temperature. This would 

 reduce the mean annual temperature here to 3?i, that of Moscow 

 and Quebec, with which the climate at the higher gravel period has 

 been before compared, being respectively 40 and 41, and would 

 agree with what has been considered the probable mean winter 

 temperature of that period, viz. one between 10 and 20. 



Taking this as the starting-point, the effect of such conditions with 

 reference to the quantity of ice and snow stored up during this period 

 of cold, and to its effect on the river-discharges for many years after- 

 wards during the period of the valley gravels, has to be considered. 

 The melting of the winter snow would necessarily cause spring floods. 

 Another cause of floods is the fall of rain whilst the ground is still 

 frozen. These causes, combined possibly with a larger rainfall, must 

 have afforded to the old rivers, either permanently or at all events 

 during spring-time, a volume of water far exceeding any present sup- 

 ply, and giving them more of a torrential character. Instances are 

 quoted from Sir R. Murchison's 'Russia' and Wrangel's 'Siberia,' 

 and others, to show how this is still the case every spring in northern 



