PORTION OF THE SCHUYLKILL COAL-FIELD. 93 



viduals, for associations, or for the community at large, — cannot 

 fail to develope new and beneficial results wheresoever directed, in 

 such a field. To have had some share in the attaining and the 

 distribution of this knowledge, and to have contributed any aid 

 to the great cause of economic geology, is a gratification which 

 is worth no small exertion to acquire. It has proved, let me add, 

 in all sincerity, the strongest inducement to perseverance in the 

 work now before the Association. 



At the request of some members of the Association, I have 

 annexed to the foregoing memoir a few illustrative sections, con- 

 structed on a variety of small scales, with the intention of exhib- 

 iting the practicability of using even minute vertical scales, in 

 geological demonstrations. They are as follows: [Plate IV.] 



Fig. A, represents a section whose horizontal scale is three miles to an inch, and 

 the vertical scale 5280 feet to the inch, being- in fact in the proportion of 3 to 1. This, 

 although less distorted than is occasionally the case, it being easy to point out examples 

 where the proportions are 6, 8, and 10 to 1, is drawn to show the contrast to the section B 

 beneath it, where the proportions are equal, the horizontal line and the area illustrated 

 being similar. 



Fig. B. Section at three miles to an inch, both vertical and horizontal, of the same 

 ground as Section A, and in fact a transverse section of a model, which has been describ- 

 ed in the foregoing paper. 



Fig. C. Section protracted at four miles to an inch, both vertical and horizontal. It 

 shows the position pf two of the detached Pennsylvania bituminous coal basins. 



Fig. D. Section at five miles to an inch. Here there is a trifling increase, amounting 

 to one half only, in the vertical scale, viz. li to 1. It also exhibits two detached coal 

 basins in Pennsylvania. 



Fig. E. Section at two miles to an inch, on equal scales. This projection is sufficient- 

 ly large to admit of characteristic details. It is a profile of the Alleghany mountain, 

 descending eastward ; also in this State. 



As I have not conveniently at hand, examples of sections hav- 

 ing the altitudes above tide level, drawn by other authorities, it 

 was^ necessary to resort to the materials which happen to be in 

 my possession, and for the most part prepared from personal ob- 

 servation.- I hope they are sufficiently accurate for the purpose 

 designed. 



To render these experimental drawings more useful for com- 

 parison, I have inserted Professor H. D. Rogers's numbers of the 

 respective formations. With regard to the colors adoptcfl, they 

 are not proposed as standards, but are simply those which I have 



