10 PROCEEDINGS OF THE COLUMBUS MEETING 



tain a nearly uniform thickness of from 4 to 6 feet or more over areas of several 

 hundred square miles. The lower beds, while often reaching from 4 to 6 feet in 

 the center of small basins, will average much helow 3 feet on account of their thin- 

 ness ever the intervening ridges. 



Structure 



The major structure of the field is that of a monocline, the dip being to the south 

 of west in the northern part and north of west in the southern part, being noticeably 

 affected by the thickening of the strata to the south. The dip is slight, averaging 

 about 24 feet to the mile, though running as high as 100 feet to the mile. 



In its minor structure the field presents a great variety of interesting features — 

 faults of many types, veins of clay, sandstone and coal, and local irregularities and 

 disturbances of many kinds. Attention has already been called to some of these 

 in the Proceedings of this Society and of the Indiana Academy of Science. 



Remarks upon Doctor Ashley's paper were made by J. A. Holmes, 

 [. C. White, J. M. Clarke, the President, and the author. 



The next paper was entitled : 



CAPE FEAR SECTION IN THE COASTAL PLAIN 

 BY J. A. HOLMES 



Remarks were made by E. T. Dumble. 



The next paper was read by title as follows : 



OCCURRENCES OF CORUNDUM 

 BY J. H. PRATT 



The last paper of the meeting was presented informally by the author, 

 entitled : 



TRIASSIC COAL AND COKE OF SONORA, MEXICO 

 BY E. T. DUMBLE 



The Santa Clara coal field of Sonora, Mexico, is situated in the Yaqui river 

 drainage, 95 miles northeast of Ortiz, near the mining town of La Barranca. 



The region is mountainous. Although the elevations in this particular area are 

 not very great, there are mountains on the north and east. Aguja, on the west, 

 has a height of 3,950 feet, while the Carrizo, which is still higher, is on its north- 

 ern border. Candelero, another large mountain, the top of which is about 3,700 

 feet above sealevel, lies between Aguja and the coal field. While there are numer- 

 ous peaks and high points scattered over the coal field, that portion of the area east 

 of Candelero is much lower than that west and is partly rolling, partly hilly. Can- 

 delero trail, which may be called the western border of the developed field, is over 

 1,800 feet in height, and Tarahumari, near its center, 1,170 feet, while La Barranca 

 in the west is 2,000 or over. From Tarahumari east the slope is considerable also, 

 the point where the Calera empties into the Yaqui being about 700 feet above tide. 



The three principal creeks are the Arellanason the north, Calera in the center, 

 and La Barranca in the southwest. The Arellanas and La Barranca are true 



