Mr. J. Ball on the Formation of Alpine Lakes. 497 



M. de Mortillet has, if I may venture to say so, done excellent 

 service to science by calling attention to the difficulties that have 

 to be explained, and by observations, in many of which he has 

 preceded other inquirers ; but he has proposed an explanation 

 which seems to me essentially defective, while he has turned his 

 eyes away from the direction whence light might have been shed 

 on the subject. 



MM. Gastaldi and Mortillet have put aside with little discus- 

 sion the belief expressed by me that the distribution of the dilu- 

 vium in the north of Italy, and its relations to the undoubted 

 remains of glacial action, cannot be accounted for without ad- 

 mitting the presence of the sea in the valley of the Po during 

 some portion of the glacial period. I have no pretension to 

 speak dogmatically on the subject, but I may say that my con- 

 viction on this subject has arisen altogether from observations 

 made during repeated excursions in the southern valleys of the 

 Alps, and has been more and more confirmed as I have found 

 that, although there may not be evidence amounting to direct 

 demonstration, each new visit to the Alps has added to the list 

 of observations which are consistent with this belief. 



In the first place, this hypothesis has in its favour no trifling 

 amount of a priori probability. There is no evidence whatever 

 pointing towards any local disturbance of level in the Alps since 

 the miocene period ; it is therefore the more probable that the 

 entire chain should have participated in any general change of 

 the relative level of land and sea that affected the adjoining 

 regions during the later geological period. We have conclusive 

 evidence to show that in those islands the sea stood during a 

 portion of the glacial period at least 1500 feet higher than it 

 now does. We know also that a considerable part of North 

 Germany was submerged, as well as a still more extensive region 

 in Northern Africa. Leaving out of account other more disputable 

 instances of recent change of level, these facts suffice, as I think, 

 to create a presumption in favour of the view which I advocate, 

 and which, if I mistake not, is supported by the high authority 

 of M. Omboni. 



One of the main reasons which makes probable the presence 

 of the sea in the valley of the Po, is the wide dispersion of the 

 diluvium throughout the great plain at the foot of the Alps. 

 The diluvium is not merely found at the opening of the main 

 valleys that penetrate deeply into the interior of the Alps ; it is 

 spread along the base of the entire range, in situations quite out 

 of the path of those imaginary currents that are said to have 

 swept the rolled debris from the valleys into the plain. In some 

 places, as on the plain of Friuli, it is spread out on a dead level 

 in a uniform stratum, without the slightest break, and with 



