86 Taylor's model of the western 



beneficial application of science in economic geolog}', form legit- 

 imate objecis of associations like that which I have the honor of 

 addressing. 



The area here illustrated comprehends seven hundred and 

 twenty square miles ; being in length forty-five miles, and in 

 width sixteen miles. It extends in breadth from four miles above 

 Harrisburg, northward, to Millersburg on the Susquehanna, at 

 the junction of the Wiconisco railroaid. In length it reaches 

 from the western extremity of the Cove mountain, on the west 

 side of the Susquehanna, to within eight miles of Pottsville. It 

 comprises the two forks into which the Schuylkill coal-field sep- 

 ai'ates, opposite to Pinegrove, in the Swatara region. The 

 northern fork or branch extends to the "Wiconisco Coal Compa- 

 ny's mines at Bear Gap, and the southern branch stretches 

 towards the Susquehanna in a southwest direction, to within 

 about a mile of that river. The coal formation along several 

 miles of the western portion of this lower fork, is reduced to a 

 narrow ridge, which can scarcely be expected to contain coal to 

 any valuable extent. Both the branches alluded to are bounded 

 or enclosed by corresponding mountain ridges; the strata of 

 which, cotnposed of the inferior red shales, and of a numerous 

 series of sandstones and conglomerates, underlie the coal meas- 

 ures and the upper red shales. The coal strata in these separate 

 branches or basins dip, for the most part, to their respective 

 centres. 



The horizontal area is protracted on a scale of two inches to a 

 mile ; the data for which have been derived from a variety of 

 public and local surveys. In the vertical scale we have been 

 enabled to approach so near to the horizontal as two of the for- 

 mer to one of the latter ; an approximation which is more close 

 than is usual in such works. And here it may be permitted to 

 apply some remarks on the construction of diagrams. . 



It has been customary with most geologists, and I believe 

 almost universally Avith civil engineers, where the bases of their 

 sections are considerably extended, to adopt a much larger scale 

 for the perpendicular than for the longitudinal dimensions. Con- 

 sequently, the diagrams so drawn, amount to absolute cUstortions, 

 and manifestly convey very inaccurate ideas. The proportions 



