248 ANNALS NEW YORK ACADEMY OF SCIENCES 



while that of Eiou Vieux at the southeast appears to owe its direction in 

 great measure to the distribution of rocks in that region. This erosion is 

 later than the middle Tertiary and, by most writers, is referred to the 

 Quaternary. All phenomena testify to its recent origin. The valleys, 

 for the most part, are narrow and the hill slopes are abrupt, while the 

 summits are clearly remnants of a plain. The granitic rock on the west 

 side has yielded much the same topography as that of the Coal Measures 

 area. The steep hillsides must have been captured early by vegetation, as 

 they show comparatively little gashing. 



The later work of removal has been confined chiefly to corrasion, and 

 erosion has done comparatively little toward leveling the region. But a 

 long-anterior erosion, probably preceding the Jurassic and following the 

 time of folding and faulting, removed the Permian and newer portions 

 of the Coal Measures from much of the basin and exposed the oldest de- 

 posits in the southeast. The Quaternary erosion increased the area in 

 which the early beds reach the surface; while trenching of the basin by 

 valleys 400 to 600 feet deep has made the coals accessible at many places 

 and rendered possible those mining operations which have attained so 

 great economical importance. 



Boisse, forty years ago, recognized at least two distinct systems of 

 deposits and suggested that the succession might be divided into three. 

 Bergeron, twenty years ago, determined the three systems, Auzits, Cam- 

 pagnac and Bourran. This division may not be supported strongly by 

 paleontological evidence, but it is sufficiently distinct, for the physical 

 conditions are unlike in the several systems. 



The Auzits system consists of a succession of conglomerates, sandstones 

 and some shales, the materials having come almost wholly from the south- 

 ern border. These deposits have been exposed by erosion, and they pass 

 under the newer rocks at a very short distance north from the Eiou 

 Vieux; but the upper beds are at the surface in' the valley of Eiou Mort, 

 on the eastern border. This system includes toward the base the Soulier- 

 Abiracs coal bed and, apparently higher, the unimportant coal deposits 

 north from Auzits known as the beds of I'Estang. 



The Campagnac system, beginning with the coal bed known as Eulhe, 

 Campagnac, Paleyrets, Bouquies, in the several localities where it is 

 worked, consists very largely of conglomerates with some sandstones and 

 shales. Its rocks are exposed in much of the eastern half of the basin, 

 and the great coal bed at the bottom is mined at many places. The con- 

 glomerates are shown frequently on the roads and, though the composi- 

 tion varies, the features are such as to show that substantially the same 

 physical conditions prevailed along most of the streams which supplied 



