Notice of a Geological Model. 91 



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 an- 

 nexed 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 : 



Fig. A, is 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 ex- 

 amples 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 the model, which 

 has been described in the foregoing paper. 



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

 It shews the position of 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. 1^ 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 

 sufliciently large to admit of characteristic details. It is a profile of the Alle- 

 ghany mountain, descending eastward ; al.so 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 adopted, they 

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

 been accustomed to employ ; differing very little, I perceive, from 

 those used by the gentleman last mentioned. 



Before closing this subject, permit me to allude to the new 

 geological map of England and Wales, by Mr. Greenough. As a 

 finished specimen of art, it is probably the most beautiful produc- 

 tion of the age, and may with great advantage, be consulted, for 

 the extreme clearness of its details. 



