276 ANNALS NEW YORK ACADEMY OF SCIENCES 



little contraction by lateral pressure; the folding and faulting of the 

 beds may be due to a different cause. Apparently, the only difiEerence 

 between present and original limits is due to the slight transgression of 

 Jurassic at the south and of andesite at the north. 



MODE IN WHICH THE BASIN WAS FILLED 



More than 20 years ago, Bergeron recognized in the Decazeville basin 

 all the features required by Fayol's doctrine of delta formations. Deltas 

 deposited in a body of deep water are subaqueous cones of .dejection, 

 whose characteristics have been discussed elaborately from the mathe- 

 matical viewpoint by Lemiere. Bergeron saw evidence of three such 

 deltas, two at the southern end and one at the northeast. Twelve years 

 later, when the careful studies, initiated under Fayol's direction and 

 conducted according to the method employed at Commentry, had led to 

 a great accumulation of facts, Bergeron, Jardel and Picandet were able 

 to prove by the included fragments the existence of at least four deposit- 

 ing streams along the southern border, of one at the northeast and the 

 probable existence of two on the western border. Their observations 

 have been referred to incidentally in preceding pages, but they must be 

 summarized here. They show the value of patient study in what too 

 many think petty matters, for the results are farther-reaching than ap- 

 pears at first glance. The writer desires to pay tribute to those students, 

 whose accuracy of observation and acuteness of discrimination provoked 

 admiration at more than one locality. 



Three streams cooperated in forming the early deposits at the southeast 

 corner of the depression, one passing near Longuefort and entering near 

 Auzits after having crossed microgranulite and mica schist ; a second at 

 less than a mile westward, entering near Haute Serre, and a third enter- 

 ing near Lugan. The especial deposit of each is characteristic and the 

 confluence of the cones is well marked. The course of the Haute Serre, 

 the most important of the brooks, is made distinct by the distribution of 

 coarse fragments for a considerable distance northward. A fourth 

 stream, entering at the southwest near Yalzergues, contributed its share 

 somewhat later in the history, while a fifth, entering at the northeast 

 near the Pont du Bourran, gave the deposits marking that portion of the 

 basin. All of these were active during the deposition of the Campagnac 

 system, and the inflowing waters found exit on the east side near Finny, 

 where elements from north and south are commingled. The western 

 streams, those entering near the Moulin du Faux and from Viviez, gave 

 no deposits in the western part of the depression until the beginning of 



