COLLEGNO ON THE LOMBARDIC ALPS. 115 



formation, and others considering the lenticulite limestone of 

 Bayonne as tertiary, without pronouncing on the Biaritz strata.. 

 It appears on first examining these localities that the limestones 

 forming cliffs between la Chambre oV Amour and Bidart are con- 

 temporaneous, although a closer examination proves that there 

 are two distinct series of different ages, so that the almost con- 

 tinuous bed which forms the cliff between la Chambre d' Amour to 

 about 1000 yards beyond the rock of Goulet, are newer than 

 those which next make their appearance, and from which they are 

 separated by a gap in the cliff. At this place it would seem there 

 has been considerable disturbance, the beds displaced being no- 

 where conformable to the limestones, like those of Bidart, however 

 nearly they resemble them ; but the nummulitic limestone observed 

 on the road from St. Pierre to Briscons is conformable to another 

 compact and crystalline limestone which is made up of fragments 

 of corals. These limestones are not found in the cliff, and they 

 ought perhaps to appear in the spot where the fracture has pro- 

 duced a gap. 



The nummulitic limestones of the Biaritz lighthouse, and of the 

 neighbourhood of Bayonne, have, however, no relation with those 

 of Bidart, for they differ from them both in structure and com- 

 position, besides being unconformable. The cretaceous strata of 

 Bidart and of the whole district west of the Pyrenees have a 

 general uniform inclination, due to the elevation of the mountain 

 chain ; but after this other disturbances have taken place, accom- 

 panied by the protrusion of igneous rock. The cretaceous beds of 

 Bidart, St. Jean de Luz, and of the whole western Pyrenees, thus 

 offer clear marks of a general elevation succeeded by partial dis- 

 turbances ; and the dislocations are most considerable where the 

 limestones are nearest the volcanic centre. The case is quite 

 different with respect to the beds of Bayonne and Biaritz. These 

 are conformable to one another, and they are very nearly hori- 

 zontal, except in the recently disturbed districts. 



It results from these geological observations that all the beds of 

 coarse sandy and marly limestone of Bayonne and Biaritz, as far as 

 the mill of Sopite, following the line of cliff, belong to a lower 

 tertiary group ; and that those occurring a little further on, as far 

 as and beyond Bidart, are of the cretaceous period. 



D. T. A. 



IV. On the Stratified Rocks of the Lombardic Alps. By 



M. DE COLLEGNO. 



[Read before the French Geological Society, Jan. 22. 1844.] 



This memoir on the structure of the Lombardic Alps presents a 

 minute detail of the geology of the district, and is accompanied by 

 sections illustrating some of the more important points. The subject 



i 2 



