Lithological Survey of Schehallien. 363 
From the inspection of the preceding table, it is evident 
that the specimens relatively to their specific gravity may be 
divided into two classes sufficiently distinct from one another. 
The specimens of granular quartz are in specific gravity com- 
prehended between 2.61 and 2 .66, nearly, and the mean is 
2.639876. The micaceous rocks, including the calcareous, are 
contained between the limit 2.7 and 3.06, the mean of all the 
15 specimens being 2.81039. Now it happens fortunately, 
that these two classes of rocks distinguished by their specific 
gravity are also distinguished by their position, so that the 
line which separates them can be accurately traced out on the 
face of the mountain. As to the arrangement of the same two 
classes of rock in the interior of the mountain, there are only 
two different suppositions, as already observed, which possess 
any degree of probability, and the result of each is hereafter 
to be given. The curve line in the plan of the mountain 
divides the quartzy from the micaceous rocks. 
I shall now proceed to state the principles on which the 
present investigation is founded, and the result to which it 
has led. 
According to Dr. Hutton's construction, if O (Fig. 1.) be 
the place of the plummet in the south observatory, ON the 
direction of the meridian, and if with a radius ON — 13333 
feet, or a quadrant of a circle be described, viz. WRN ; 
if ON be divided into 20 equal parts, and if from O as a 
centre, through each of these points of division, circles be 
described : lastly, if through O, radii as OH, OG, See. be 
drawn such that the sine of the angle which each of them 
makes with the meridian shall differ from the sine of that 
3 A2 
