Le cours supérieur du Loir et le contact entre Perche et Beauce

Abstract

The lie of the middle course of the Loir, running from NNE to SSW, from Bonneval and even Alluyes, as far as the bend at Vendôme, has been very satisfactorily explained, but it is not the same with regard to its upper course which, from its sources to Alluyes, presents a curious bayonet-shaped lie which also demands an explanation. Having recalled that the hypothesis of a deviation (« capture ») has been put forward to explain the bend that the upper Loir describes at Fruncé where the river, at first flowing from West to East, makes a sudden right-angled turn, to flow North-South, the author is brought to look for other reasons for this change of direction, and at the same time he explains the broken lie of the river further South ; also the sudden changes in size that its valley undergoes in several places. Three sections of different direction follow, from the Fruncé bend to Alluyes : a North-South section, to which corresponds a wide, dissy- metrical valley, is set in a groove which most likely accompanies a meridional fault marking the eastern end of the Perche bulge ; a NE-SE « capture » section, grafted on to Plaisance along the Loir-Thironne waterway ; a section running WNW - ESE, connected at Alluyes to the middle Loir, which was originally simply the lower course of the Thironne, today a tributary of the Loir.