GENEVA SOCIETY OF PHYSICS AND NATURAL HISTORY. 205 



Ernest Favre, de Loriol, de Saussure, and Soret, to arrange this mat- 

 ter. This committee, which had the power of adding new members, 

 was commissioned to take measures for the reception of the Geological 

 Society during its stay in Geneva. 



RESUME OF SCIENTIFIC WORK. 



1. Physical sciences. — Professor Colladon read before us a memoir in- 

 serted in No. 212 of the Archives des Sciences Physiques et Naturdles 

 (Archives of the Physical and Natural Sciences), October, 1874, on the 

 vestiges of a former bed of the Arve, discovered by digging for the found- 

 ations of the new theater. The excavations made on this occasion, at 

 the foot of the terraces of Treille and Tertasse, disclosed the presence 

 of a bank of gravel and sand from 2.1 to 2.5 metres (7 to 8 feet) in depth, 

 lying on a bed of clay whose upper surface is 0.85 metre (33 inches) below 

 the mean level of the^waters of the lake at the present time. The orienta- 

 tion of the stones and pebbles forming this bank indicates that it must 

 have been deposited by a current flowing from the southeast toward the 

 northwest, and the chemical and mineralogical composition of the sand 

 is absolutely identical with that of the sand now drifted by the Arve, 

 and proceeding from the rocks forming the chain of Mont Blanc. There 

 can then be no doubt that at the era when this deposit was formed, the 

 Arve emptied into the Rhone, very near its issue from the lake, and 

 within the inclosure of the present city, whereas the confluence is now 

 more than a kilometer (about a mile) down stream. The existence of 

 this bank of gravel and sand, at different points of the plain of allu- 

 vium, comprised between the city and the present bed of the Arve, had 

 already been established on several occasions ; and it might therefore 

 be concluded that the direction of the current of the lower portion of 

 the Arve has gradually changed in the course of centuries, and that 

 after flowing by the foot of the hill, on which the most ancient part of 

 the city is built, the river empties into the Rhone at the foot of the hill 

 on which the forest of Batie is found. The era to which the deposit of 

 gravel mentioned by M. Colladon dates back does not appear to be very 

 remote, not exceeding twenty or thirty centuries, as within the interior 

 of these ancient strata, which have never been touched, are found frag- 

 ments of bricks, and even pieces of wrought iron very much rusted. 

 The fact that the upper surface of this deposit is about 1.5 metres (5 

 feet) above the mean level of the waters of the lake at this present 

 time is mentioned by M. Colladon as proof that this level must have 

 been sensibly higher by at least two metres (G^ feet) at the period of its 

 formation. 



Dr. F. Florel communicated a memoir, inserted in No. 205 of the Ar- 

 chives, January, 1875, on the configuration of the bottom of Lake Le- 

 man, in accordance with the four maps of the topographical atlas of 

 Switzerland, published by the Federal Bureau of the Staff Office. These 

 four maps, drawn on a scale of 25 Joo, according to the notes and sound- 



