260 Dr. Berger on the Geology of some Parts 



The speciGc gravity of the different specimens of this limestone, 

 I have found to be as follows : 



From the Z/W^r 67/^ in the Isle of Wight . . ^fi6Q 



From Steeple Ashton, Oxford 2,624 



Wind Spit quarry 2,592 



Swanage 2,563 



Portland N.E. quarry 2,563 



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 j a range 

 much less than is stated by M. Brongniart from Rondelet's experi- 

 ments, viz. of 24 : 17.* 



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 Tiliy 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. 



* Traite elementaire de Min.ral. tome i. p. 208. 



