COAL-FIELD OF CLACKMANNANSHIRE. 149 



much higher; but whether it was ever complete- 

 ly of a conical shape, is now impossible to determine 

 Hurst Hill, which lies to the westward of the two 

 hills before described, is similar in its structure to 

 those already described. Excepting where these 

 hills occur, forming the strata into the inverted ba- 

 son shape, the great Staffordshire coal-field is of the 

 true bason form, The strata betwixt and under the 

 beds of limestone, is named by the miners Bavin. 

 It is a grey-coloured, indurated clay, with a mixture 

 of lime in its composition, and contains numerous 

 small bivalve shells. Plate V, No. 5. is a section 

 of this astonishing coal-field, the upper coal of which 

 is 30 feet thick ; and this coal extends seven miles 

 in length and four in breadth. Coals of five and six 

 feet in thickness, are there denominated Thin 

 Coals. 



The whole of the strata connected with the beds 

 of limestone, forming the lower series of the strata 

 of this most interesting coal-field, abound with nu- 

 merous organic remains of the animal and vegetable 

 kingdoms ; in particular, Molluscse, Madrepores, 

 Corals, and casts of a singular animal, termed by the 

 miners a Locust, but known to naturalists by the 

 name of Pediculus marinus, or the Dudley Fossil. 

 It is, I believe, only found in that district, and we 

 know of no recent species now existing. There are ' 

 also numerous bivalve shells ; and in the slate-clay, 

 more immediately connected with the coal, are . 

 numerous impressions of Filices, Equiseta, Reeds, 



