The specific gravity of the different specimens of this limestone,
I have found to be as follows:
| From the Under Cliff in the Isle of Wight | 2,666 |
| From Steeple Ashton, Oxford | 2,624 |
| Wind Spit quarry | 2,592 |
| Swanage | 2,563 |
| Portland N.E. quarry | 2,568 |
| Tilly Wym quarry, passing to a calc. sandst. | 2,466 |
| ───── | |
| Mean spec. grav. | 2,579 |
The ratio between the extreme points, is as 92 : 100; a range much less than is stated by M. Brongniart from Rondelet's experiments, viz. of 24 : 17.[1]
The specific gravity of the compact hard bluish limestone found in patches in the coarse shelly limestone, I have ascertained to be as follows:
| From Tilly Wym quarry | 2,501 |
| From Portland | 2,511 |
| ───── | |
| Mean | 2,506 |
Lastly, the specific gravity of a dark-blue flint or chert, from Portland, connected with the bluish compact limestone, and passing gradually into it, is 2,545.
In the quarry of Tilly Wym, the flint or chert is mostly under the form of detached masses or nodules; while in the under cliff in the Isle of Wight, and in the Isle of Portland, it forms continuous layers; in the latter place, their direction is that of the strata, viz. nearly from north to south, their dip being east by south.
- ↑ Traité élémentaire de Minéral. tome i. p. 208.
