152 PROCEEDINGS OF THE AMHERST MEETING 



CONSTITUTION OF THE OHIO BLACK SHALES 

 ' BY GEORGE H. CHADWICK 



Presen ted extemporaneously. 



Discussed by Arthur Keith, Charles Schuchert, J. W. Beede, and 

 T. W. Vaughan. 



Discussion 



Professor Schuchert : The speaker agrees with Doctor Keith that the 

 stratigraphic correlations made by Professor Chadwick could not have been 

 made on the basis of fossils alone. We see here the fine results attained when 

 fossils are used to check the tracing of formations from place to place. This 

 detailed local tracing of the various formations leads to the fixing of times 

 of erosion and overlap, and to a determined and provable stratigraphy and 

 paleogeography. 



VOLCANIC ASH BED IN THE ORDOVICIAN OF TENNESSEE, KENTUCKY, A\D 



ALABAMA 



BY WILBUR A. NELSON 



(Abstract) 



A discussion of the occurrence of a deposit of volcanic ash known as ben- 

 tonite and consisting mostly of leverrierite. The bed occurs at the top of the 

 ('arters formation of the Black River group of the Ordovician. Descriptions 

 of outcrops from Birmingham. Alabama, on the south, to Highbridge, Ken- 

 tucky, on the north, will be given and the economic possibilities of this deposit 

 discussed. 



Read from manuscript. 



Discussed by Charles Schuchert, T. Wayland Vaughan, and G. H. 

 Ashley. 



Discussion 



Professor Schlchert: The speaker wishes to congratulate State Geologist 

 Nelson on his very remarkable discovery of this widely spread ash bed of 

 Lowville age. covering an area estimated at more than three hundred thousand 

 square miles. As the time of this ash-spreading was very limited, possibly of 

 only a few years' duration, and since it is the only one known in the Mo- 

 liawkian series, this ash zone is one of the finest possible time-markers, more 

 limited by far than any faunule can be. 



Dr. Vaughax mentioned the value of widely extended thin ash beds in pre- 

 cise correlation. 



Dr. Ashley called attention to the possibility of a distribution to account 

 for the occurrence of thin clay beds making pastings in coal beds, some of 

 which maintain uniform thickness over thousands of square miles. 



