Page:Natural History Review (1862).djvu/64



town of Aurignac, situated in the arrondissement of St. Gaudens (Haute Garonne), is placed nearly on the summit of one of five eminences, constituting a hilly range, whose geognostic formation and upheaved strata manifest its relations with the dislocated spurs of the Pyrenean system. The contour of this oreographic projection, in which the strata of the chalk and of the nummulitic or supracretaceous rock are not always inclined in the same direction, differs but little from that of the tertiary hills which rise below it to the west. The confused and uninformed traveller, consequently, approaching Aurignac firom that side, would not perceiye the transition which is manifested under his feet, were not his attention awakened by a sudden change in the nature of the rocks and by the evidences of dislocation presented in the road-cuttings.

The road leading from Aurignac to the little town of Boulogne in the same arrondissement, runs pretty nearly from east to west, on the southern flank of the mountain of Portel. On the opposite side, to the south, rises the mountain of Fajoles, forming an elongated, saddle-shaped ridge, which runs in pretty nearly the same direction, and which, though of lower eleyation, and nowhere precipitous, is nevertheless completey isolated from all the hydrographic influences of the district. Between these two eminences, or mountains, is a contracted yalley along whose bottom runs the brook of Rodes or Arrodes, which, on reaching, a littte more to the west, the foot of the mountain of Portel, turns sharply round to the north, aud after running a few kilometres to the north-west joins the Louge, a small riyer which takes its rise on the plateau of Lanemézan.