940 



GEOLOGY OF OHIO. 



appended to show the general structure of the seam. The samples wer« 

 taken at intervals of about one foot, and are numbered from the top 

 downward. 



STRUcfTDEi; OF thS Great Skam at Steaitsville. 



rr. IN. 



1. Coal. 2 



2. Parting 2 



3. Coal 2 



4. Parting.. 4 



5. Coal 4 



6. Clay parting 6 



7. Coal 2 



The analyses are as follows : 



The average percentage of sulphur is 1.12. 



A few words will be added in regard to the determination of the dip of 

 the strata. Many determinations of direction and amount have been 

 made in different parts of the district during the progress of this exam-' 

 ination, but the want of space excludes them from the present report. 



A graphic method of determining this important factor in geological 

 exploration, has been kindly furnished by Prof. R. W. McFarland, of the 

 Ohio State University. It has been found so intelligible and so service- 

 able, and is so -simple and beautiful withal, that it is appended here. 

 It is a valuable contribution to stratigraphical geology. By the aid of a 

 map on which the elevations of definite horizons, like coal seams or lime- 

 stones, are marked, the direction and amount of dip can be readily de- 

 termined. The excellent map of the Hocking Valley coal field, by W. 

 H. Jennings, Esq., of Columbus, gives numerous elevations of the great 

 seam above Lake Erie, which can be used in these calculaticjns. 



A Graphic Method of Determining the Direction and Amount of Dip in Coal 



AND EoCK Strata. 



"Join on the map three points in some stratum, the elevation of these points above a 

 given base (e. g. Lake Erie, or tide-water) being known, or make a triangle similar to 

 that on the map. Find the elevation of each of the two higher points above the lowest ; 

 at right angles to the line joining the two higher points, set oif their respective heights 



