FOR DETERMINING THE MEAN DENSITY OF THE EARTH. 
339 
where (as has been explained in article 46) the last term ought probably to be 
doubled^ to give the uncertainty depending on the pendulum-experiments only. 
Section VIII. — Estimation of the Mean Specific Gravity of the Surface Rocks ; and 
final conclusion on the Mean Density of the Earth, as determined from the Pen- 
dulum Experiments. 
61. By the kindness of Mr. Arkley, I was furnished with a complete account of 
the strata passed through in sinking the Harton shaft, and with specimens of a great 
number of the rocks. These were submitted to Professor W. H. Miller, who with 
great labour determined their specific gravities. I place below the entire catalogue 
and measure of the strata, and the results at which Professor Miller arrived. Pro- 
fessor Miller remarks that there is inevitable uncertainty in the estimation of the 
weight of those specimens which were drawn from beds described as containing 
water. 
No. 
Description of Rock. 
Thickness. 
Specific 
Gravity. 
Tempera- 
ture of 
water, 
Centigrade. 
1 
ft. 
1 
in. 
0 
0 
2 
Yellow Clay 
6 
4i 
3 
Blue laminated Clay 
7 
o“ 
4 
Gravelly Clay 
69 
2 
5 
Red Clay (resting on the Stone Head) 
10 
0 
6 
Soft blue Shale, and a little Water 
7 
0 
7 
Coal ’ 
3 
8 
Dark Grey Shale 
7 
6 
2*5698 
15*9 
9 
Coal " 
3 
10 
Dark Grey Shale 
12 
3 
2*5273 
16*4 
11 
Coal and a little Water 
4 
12 
13 
Stronff dark Grev Shale mixed with Sandstone 
9 
2 
Strong Grey Sandstone and Water 
7 
10 
2*5341 
8*8 
14 
Grey Shale 
18 
0 
2*6170 
9-2 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
Bituminous Shale 
5 
Coal ’ 
1 
0 
Thill or Grey Shale 
4 
2 
Sandstone Girdle. 
10 
Grey Shale, Sandstone Girdles, and Water 
14 
2 
White Sandstone Girdle and Water 
1 
2 
Grey Shale 
1 
6 
White Sandstone Girdle and Water 
3 
5 
Bituminous Shale 
2 
9 
Coal 
4 
Thill or Grey Shale 
10 
0 
2*5325 
9*7 
Grey Sandstone 
3 
2 
2*6325 
9-5 
Grey Shale 
2 
6 
Grey Sandstone with partings of Bituminous Shale 
2 
8 
Blue Shale 
5 
8 
1 
2 
Dark Grey Shale 
4 
6 
32 
33 
Grey Shale 
10 
0 
1 
2 
34 
Band of Grev Shale 
4 
35 
Coal 
6 
36 
Sandstone with very hard Girdles 
7 
0 
2*8072 
17*25 
2 Y 2 
