396 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 9, 



2. On the Effects of Glacier-Erosion in Alpine Valleys. 

 By Signor B. Gastaldi, F.C.G.S. 



(Translated from a letter to Sir Charles Lyell, and communicated by permission 

 of Prof. Grastaldi.) 



I have all the more pleasure in answering your kind letter, that I 

 have for a long time been waiting for an occasion to write to you, 

 and to send you some geological notes which I have published 

 during the last few years. 



For seven years I have been working at a geological map of the 

 Piedmontese Alps, on a scale of g o^ ou ; and for the last three years 

 I have been aided in this work by Professor Baretti. The great 

 scale of the maps on which we lay down our work, does not permit 

 us to rapidly survey a very extended area ; so that in seven years 

 we have only succeeded in completing the valley of the Oreo, com- 

 prising the group of the Grand Paradis, the three valleys of 

 Lanzo, including the groups of the Levanna and of Boccia Mellone, 

 and the valley of the Dora Biparia, comprehending the heights of 

 Mont Cenis, the Frejus, Tabor, Mont Genevre, Bochesmolles, &c. 



Chance led me to pass my holidays in the Alps, where I began to 

 survey geologically the valleys of Lanzo, and ended by taking a fancy 

 for Alpine geology — unhappily a little late ; for I am growing old, 

 and the geology of the Alps on a scale of -g^-^ is rough work, 

 which cannot be done without walks very fatiguing to a man of 

 fifty-five. From the beginning of my work I noticed in the valleys 

 of Lanzo, and at heights between 2000 and 3000 metres, hollows 

 in the form of amphitheatres or great cirques, which have generally 

 a shape like the interior of an armchair, or, more elongated, like a 

 sofa. The back of the armchair is formed of scarped walls cut in 

 the thickness of the mass of the mountain, the two sides by ridges 

 which descend from the mountain ; and the part which answers to 

 the seat of the chair, is formed by the inclined slope of the moun- 

 tain, the surface of which is moutonnee, often striated, and here 

 and there covered by the debris of moraines. 



I did not at first attach much importance to this fact, as you 

 yourself and other geologists have admitted that glaciers can, and 

 indeed have deeply excavated the rocks over which they flowed in 

 the heights of the Alps. However, having seen that Mr. Bonney 

 has forestalled me in publishing the same observations (Journal of 

 the Geological Society, 1871) founded on the same facts observed in 

 other Alpine regions, it was my wish to repeat my own observations 

 in the high valley of Susa. 



This year in the valley of the Biparia I have found the same facts 

 on a larger scale. First I visited one of these high cirques on the 

 west slope of the Segures. I found two others in the high valley of 

 Sauze de Gesanne, where the upper branch of the Dora Biparia de- 

 scends. In the first the snows, towards the end of the autumn, have 

 completely disappeared ; in the two others we see a glacier reduced 

 to its smallest dimensions. Some of the high cirques or amphi- 

 theatres have been cut in limestone, gypsum, or eargnevle, and others 



