NEW VICKSBURG (OLIGOCENE) MOLLUSKS FROM 



MEXICO 



By C. Wythe Cooke 

 Geologist, United States Geological Survey 



The fossil mollusks described in the following pages were obtained 

 in November, 1920, by Dr. T. Wayland Vaughan from the Alazan 

 clay at and near the type locality on Rio Buena Vista, in Vera Cruz, 

 Mexico. It was intended to include the descriptions, which were 

 written in 1921, in a comprehensive account of the stratigraphy and 

 paleontology of the area covered by Doctor Vaughan's investiga- 

 tions, but as some of the papers by other authors that were to have 

 been included in that report are not yet written this contribution is 

 published in advance of the others. Thanks are due to the officers of 

 the Aguila Oil Co., who presented the collections to the United 

 States National Museum and who have generously given permission 

 to publish all the scientific results of Doctor Vaughan's expedition, 

 and to the Director of the United States Geological Survey for per- 

 mission to study this collection as part of the writer's official duties. 



The illustrations are from photographs made by Mr. W. O. Hazard 

 and retouched by Miss Frances Wieser. 



The Alazan clay was originally described by Dumble ^ as follows : 



Whether the fossiliferous shales at Alazan are an integral part of the lower 

 liard blue shales or are unconfonnable upon them has not yet been fully 

 determined, but they are probably later and are certainly upper Eocene. 



The type locality of the Alazan shales is on the Buena Vista River at the 

 crossing of the road between Alazan and Moyutlan. 



At this place the stream has cut down to the blue shales and exposed that 

 formation along its western bank and in the bed of the river for a distance 

 of more than half a mile. Overlying the shales to the west is a hill of yellowish 

 clay, probably Oligocene. On the east side of the river there is a broad valley 

 covered to a depth of 20 feet or more with recent deposits. 



The general body of the blue shale seems to have been but little disturbed ; 

 for the most part it is smooth and evenly bedded and has a low dip to the 

 southeast. Three hundred yards below the crossing there is a limited area 

 which shows the surface of the shale more or less disturbed and broken, and 

 it is here that the fossils occur. In places it appears as if small basins or 



^Durable, E. T., Geology of the northorn end of the Tampico Embayment area: Califor- 

 nia Acad. Sci., Proc, ser. 4, vol. 8, pp. 141-142, 1918. 



No. 2731. -Proceedings U. S. National Museum, Vol. 73, Art. 10 



7S959— 28 1 



