142 Proceedings of the 



this point, which is situated very low, and the Crabere, the absolute 

 height of which is 2634 m ; because, in such a case, the variability of 

 the refraction sensibly affects the zenithal distances employed in the 

 calculation of the differences of the levels. This has induced M. 

 Corabceuf to adopt the summit of the Crabere as the point of com- 

 parison between the levels of the sea and ocean. His admeasure- 

 ments were made by the southern direction of the intersection of the 

 triangle, by the northern ditto, and by the diagonals ; the mean 

 result of these admeasurements gives, for the height of the Cra- 

 bere . . above the Mediterranean . 2633 m 50 

 above the Ocean 2632 77 



Difference . . O m 73 



Another series of calculations proves that the greatest probable 

 error in the admeasurements is, for the southern, l m 860 ; for the 

 northern, l m 421 ; and, for the diagonals, l m 416; so that, even if 

 there be any difference in the level of the Mediterranean and the 

 ocean, it must be less than one of the above errors, since, according 

 to the theory, the probability of that extreme error existing is only 

 150:000. The principal of the absolute heights determined in 

 metres are the following : 



ra 



Bugarach . . . 1230.64 



Canigou .... 2785.23 



Pic du Col de Liouses . 2831.61 



Pic Oriental du Col Rouge 2805.81 



Pic d'Appi, St. Barthelemy . 2348.83 



Moncal .... 3079.51 



Lisserateca 1408.58 



m 



Picd'Ani . . . 2504.25 



Orhi .... 2016.63 



Pic du Midi de Bigorre . , 2876.74 



Troumouse . . . 3086.25 



Montespe . . . 1848.56 



Maupas . . . 3110.15 



In a subsequent part of the memoir, M. Corabceuf has rectified 

 an error of Delambre, who had supposed that there existed a differ- 

 ence of 3 toises in the height of the summit of Salces, as taken at 

 Montjoin and at the marsh of Leucate. The fact is, that the height 

 of the point above the Mediterranean is . . 362.26 toises. 

 and above the Ocean . 361.81 



Difference . . 45 



Thus affording an additional proof that the two surfaces may be 

 considered as forming one level. This work will form part of the 

 new geometrical description of France; and from its lucid details, 

 minute calculations, and important geodesical researches, was con- 

 sidered by the Academy as deserving of insertion in the ' Recueil 

 des M&noires des Savans Etrangers.' 



I 



GEOLOGY. 



Terrains Tertiaires. On the 26th March, M. Reboul, a corre- 

 sponding member of the Institute, read a memoir, the object of 



