_my possession, and for the most part prepared fro 
sane 
Notice of a Geological Model. am 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 associaten, 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, 
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 ah erse section oF the model, which 
has been described i in ne foregoing paper. 
ig. C. Section pr ed at four ellen to an inch, both wibiial and horizontal 
It shews the peiton of eg 4 the apres Pennsylvania bituminous coal basins. 
Fig. D. iles to inch. Here there is a trifling increase, 
s- 
amounting ae one "half sa in the Petia} scale, viz. 14 to 1. It also exhibits 
two detached coal basins in Pennsylvania. ‘ 
Fig. E. Section at two miles to an inch, on equal scales. This Periertion is 
sufficiently large to admit of characteristic details. ra is a a profile of the Alle- 
ghany mountain, descending eastward ; also in 
As I have not conveniently at hand, ae sections hav-- 
ing the altitudes above tide level, drawn by other authorities, it 
was necessary to resort to the fiintoctate “which happen to be in 
personal ob- 
servation. I hope they are sufficiently accurate for the purpose 
designed. - 
To render these experimental siete ae 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 ast I perceive, from 
the extreme clearness of its details. 3 
