Vol. VIII] DUMBLE— GEOLOGY TAMPICO EMBAVMENT AREA 141 



The thickness of the Chicontepec probably exceeds 2,000 

 feet. De Golyer'^ cites fossils from the Tamijuin well from 

 depth of 3150 feet which are said by Hopkins and Belt to have 

 a decided Tertiary aspect and fossils from 2900 feet in Ganahl 

 Well No. 1 at junction of Moctezuma and Tamuin rivers which 

 were pronounced Tertiary by Dr. Hart. While the fossils are 

 not named it is known that nummulites occur in the blue gray 

 marls on the Tempoal River, as in other places in the Chiconte- 

 pec, and it is, therefore, probable that the shales penetrated in 

 these two wells are Tertiary, as stated, — but they are not 

 Papagallos. 



It has been suggested that in this region these Tertiary beds 

 occupy a deep synclinal, none of the wells having reached the 

 Cretaceous beds which are found so much nearer the surface to 

 the east and west. 



Alaaati 



Whether the fossiliferous shales at Alazan are an integral 

 part of the lower hard blue shales or are unconformable 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 Oligo- 

 cene. 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 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 potholes 

 8 to 10 feet in diameter had been eroded in the underlying shale 

 and the fossil-bearing blue clays laid down in them. At other 

 places the fossiliferous beds seem broken and piled together in 

 every direction. The entire fossil-bearing area is not more than 

 200 feet in length and a few hundred yards below this the main 



"Trans. A. I. M. E. LII, p. 266. . 



