38 ECONOMIC GEOLOGY OF AMITY QUADRANGLE, PA. 
25-foot interval. Moreover, such a representation would be mislead- 
ing to the reader, who would be led to believe that the elevation at any 
given point was accurate within 25 feet, which would not be the case. 
In general, then, the limit of error for any area is not greater than the 
contour interval. 
This point has an important bearing on the structure of the Amity 
quadrangle as represented by the contours. With the exception of 
those in the Zollarsville gas field, nearly all the wells in the quadrangle 
were drilled years ago, at a time when records were generally kept 
poorly, or not at all, and in some parts of the quadrangle, on account 
of the unreliability of many records and the absence of wells, no figures 
are available to determine the depth of the Pittsburg coal, or to check 
surface tracings and correlations. It must be remembered, also, that 
the intervals between the surface rocks and the coal are irregular, as 
explained on page 42. Consequently there are few parts of the quad- 
rangle for which it would be safe to say with certainty that the con- 
tours on the Pittsburg coal are accurate enough to justify a 25-foot 
interval. The closer interval in the Claysville quadrangle, to the west, 
was made possible by the greater abundance and recency of the drill- 
ings, and also by the fact that in that area the more expensive but 
somewhat more accurate method .of leveling with the spirit level to 
outcrops and wells was used. 
STRUCTURE IN DETAIL. 
In order to show the relations of the structure in this quadrangle 
with that in adjacent regions to the east and south, PL III has been 
prepared, giving by contour lines the lay of the Pittsburg coal in the 
Amity, Brownsville, Rogersville, Waynesburg, and Masontown quad- 
rangles. This plate shows that the general structural features con- 
sist of broad anticlines and synclines, which are most prominent along 
the eastern border of the Appalachian basin and which become 
gentler in dip and less continuous toward the west. 
STRUCTURE OF PITTSBURG COAL. 
The geologic structure of the Amity quadrangle as represented 
by the deformation of the Pittsburg coal is shown in PI. I (pocket). 
The principal features are three anticlines and two synclines, all 
trending in a general northeast-southwest direction. These will be 
described in order from east to west. 
BELLEVERNON ANTICLINE. 
This was called the Waynesburg anticline by J. J. Stevenson in 
his report published in 1876 a . He also applied the same name to the 
syncline lying west of the anticline. When the Brownsville quad- 
a Second Geol. Survey Pennsylvania, Kept. K. 
