940 GEOLOGY OF OHIO. 
appended to show the general structure of the seam. The samples were 
taken at intervals of about one foot, and are numbered from the top 
downward. 
STRUCTURE OF THE GREAT SEAM AT STRAITSVILLE. 
‘ FT. IN, 
TS Coals shed oe ea ed a 0 aI AS EUG A RN Lg pe 2 oe 
Be ARAL UUM io ei oy ee UES, 2. SSI RIG om Lae Sato ve as pn oo a 2 
B55 {Coal en. saps get ok. GRR Oe are ieee SE ls Ow Lead Cane! Pate 2 he 
4. Parting. |: 2 couche Met Oe Wes Gee ee Seas ON Oe Be reset eS eR 4 
5. sCoahe eect calets ears Cees Toda oe wie ee eth cles aan ni ed a 4 ae 
6.) (Clay parting 2 les eho SCS RAE Se NAS ta yaoueUR R  rn 6 
Te? Roslas ee Saale eke SE aS BEES FR I ee sf 
The analyses are as follows: 
RO) | | LUG | 
33.99 | 31.66 
58.35 | 61.22 
ae 9.98 6.01 3.99 
30.05 | 31.37 | 31.12 | 35.03 
57.70 | 59.61 | 53.04 | 56.94 
Ashi case ema 2.04) 2.56] 6.75 3.04 | - 9.83 4.13 
100.00 | 100.09 | 100.00 | 100.00 | 100.00 | 100.00 
Sulphurieee cs soeee ee 1.02 62 94 98 71 1.04 
1.28 1.27 
1.32 127) 127) 1.30 
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 ofa 
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, Hisq., of Columbus, gives numerous elevations of the great 
seam above Lake Erie, which can be used in these calculations. 
A GRAPHIC METHOD OF DETERMINING THE DIRECTION AND AMOUNT OF DiP IN COAL 
AND Rock 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 off their respective heights 
