Mar. 14, 1872J 



NATURE 



379 



should have acted as a breakwater), the south-east and 

 north-west ridges again resume between the valleys of 

 the Essonne and the Eure. 



After the contour of the surface produced by this cxta- 

 clysm, and by which M. Belgrand considers thit all traces 

 of any previous river courses must have been obliterated, 

 the Seine and its tributaries began to flow at an elevation 

 estimated by him of from 80 to 100 feet above the present 

 level. This he proves, as we have already done, by the 

 occurrence of the remains of land mammalia and of river 

 and land shells in beds of Drift at that elevation above 

 the Seine on some of the hills near Paris. This part of 

 M. Belgrand's work is admirably illustrated^ both by 

 general and local sections, and contains valuable lists of 

 the mammalian remains, in the determination of which 

 he had the advantage of the high authority of the late 

 M. Ed. Lartet. Here again we cannot, however, agree with 

 him in his modus operandi. The great boulders of sand- 

 stone, meuliere, granite, &c., found in the valley gravel of the 

 Seine, are attributed by IVI. Belgrand in the first place to 

 removal to the line of the Seine valley by diluvial action, 

 and subsequently to their drifcing along the valley channel 

 by the river action during floods of the Quaternary 

 period, and he gives some remarkable instances of the 

 power of water to remove large blocks, and of the rate at 

 which such blocks move. When, however, it is considered 

 that the granitic rocks of the Morvan have been tran- 

 sported some 150 miles, and other rock boulders in propor- 

 tioa, that the angles of many of the large blocks of sand- 

 stone and of meuliere constantly show little wear, and that 

 they are-dispersed irregularly and at various level?, some 

 imbedded in soft clays, and others in sand or fine gravel 

 and that these latter are often twisted and contorted, we 

 can only explain the phenomena by the action of river ice 

 and transport thereby. 



M. Belgrand, on the other hand, shows that a prolonged 

 and steady fall of rain, even if not very heavy, during the 

 winter, now produces great floods — that such rivers as the 

 Yonne and Cure flowing over impermeable strata are sub- 

 ject to sudden and great freshets after a heavy but short 

 fall, whereas the Marne and Seine flowing over permeable 

 strata have their floods retarded, but, at the same time, 

 rendered more permanent by the rainfall having to pass 

 through the strata and delivered in springs. He also 

 shows that when the permeable strata become saturated 

 by long-continued rains, they act as impermeable strata 

 and that the floods follow close on the rainfall besides 

 being long maintained, so that in the remarkable and 

 long wet winter seasons of 1658 and 1802 the Seine rose 

 at Paris in the one case 29 feet, and in the other 24;^- 

 above its ordinary low level, and the floods in the last 

 case lasted three months. M. Belgrand considers that 

 this state of things was a normal condition during the 

 Quaternary period, and he sees reason to believe that the 

 rainfall at that period must have been very much greater 

 than at present. 



The ordinary low-water discharge of the Seine at Paris 

 is 75 cubic metres per second ; but during these great 

 floods it rose to 2,400 and 2,000 cubic metres. M. Bel- 

 grand gives a list of eight such floods in the last two 

 centuries, during which the discharge was above thirty 

 times greater than the ordinary low-water discharge. In 

 rivers flowing over more impermeable strata the difference 



is still greater ; and he mentions that in the Loire at 

 Orleans it has amounted to as much as 400 times, or 

 25 : 10,000. We may take the width of the Seine valley 

 during the high-level gravel period at six kilometres, and 

 during the low-level gravel period at about two kdometres ; 

 and M. Belgrand estimates that the river in flood had in 

 the first instance a sectional area of 60,000 square metres, 

 and in the second of 40,000 metres ; and, calculating the 

 flow at a given rate persecond, the discharge, as compared 

 with that of the present river, would be as under : — 



Discharge per second of the Seine at Paris in the present 

 period and during floods in past periods : — 



Present River 



low water . 

 flood-water 



8-Si 



OldRiverduringthe ( low level stage 20 \ 

 Quaternary period ( high level stage 13 



lie Metres 



• 75 

 . 2,400 



27,000 



to 

 60,000 



Large as these Quaternary period quantities are, M. 

 Belgrand thinks that there are cases of recent occurrence 

 to prove that it is possible to realise them. He men- 

 tions a flood following on a heavy rainfall in the valley of 

 the Arman(;on, a small river flowing over impermeable 

 strata, with a basin of only 1,490 square kilometres, which 

 had its discharge raised for a short time to 800 cubic 

 metres per second ; and he infers that under like condi- 

 tions of rain and impermeability (by saturation and 

 otherwise) the Seine, with its basin of 78,600 square kilo- 

 metres, might have its discharge raised to 42,444 cubic 

 metres, showing, that notwithstanding the size of the old 

 river channels, the area drained during a period of 

 greater rainfall would have sufficed for the necessary 

 water supply. 



In confirmation of this larger and more permanent 

 supply of water, M. Belgrand instances the presence of 

 the Hippopotamus, the remains of which are found at 

 several places in the Seine basin as well as in that of 

 the Somme, and which would have required for its 

 existence larger and fuller rivers. He also derives a 

 further argument in the presence of this animal, against 

 a prolonged and severe winter cold, which lie considers 

 would have been fatal to it. M. Belgrand, nevertheless, 

 argues that the presence of the Reindeer indicates the 

 six summer months temperature of Scandinavia, not ex- 

 ceeding in the mean 8^ centigrade ; but with such a sum- 

 mer temperature we hardly see how he can avoid the 

 three months' winter temperature of the same latitude 

 or of 46 per cent. A still more e.xtreme winter tempera- 

 ture is in fact indicated by the presence of the Musk Ox 

 and the Marmot. It is to be observed also that the Rein- 

 deer at that time lived as far south as the Pyrenees, and 

 that the physical condition of the drift deposits are, as 

 we have before shown, strictly in accordance with a very 

 low winter temperature. As the Hippopotamus is an ex- 

 tinct species, we do not know how far it may, like the 

 extinct Elephants and Rhinoceroses, have been adapted to 

 live in a severe climate. M. Belgrand's work is full of 

 interesting details of the distribution of these and the 

 other Quaternary animals, not only over the Seine Basin, 

 but in some cases over the whole of France. He gives also 



