Geology of Coalbrook Dale. 427 



dinate to beds of sandstone. At Lilleshall the deposit is much thicker than 

 at Steeraways, being 60 yards, and it is also purer and generally of a lig-hter 

 colour. The upper beds are dark gray and the lower nearly white; but they 

 are all subcrystalline and hard. The partings between them are frequently 

 composed of a red ochrey clay, which generally colours both the broken 

 limestone and the workmen's dress. The following is a rough list of the 

 strata at Lilleshall given me by Mr. Bolls : 



Thickness. 

 Local Names. Yds. Ft. In. 



1. White grit Thinly laminated, light-coloured and mottled, coal-measure 



sandstones variable. 



2. Gold lumber Yellow clay 1 6 



3. Grum Nodular layers of crystalline limestone, with thin seams 



of clay ; they become more compact in descending. .500 



4. Slum Red ochreous clay 1 6 



5. Grum Same as No. 3 1 6 



6. Splother Gray impure limestone 4 



7. Slum Red clay 9 



8. Riding quarry Gray limestone 1 1 6 



9. Red limestone Light red limestone ? 1 1 C 



10. Limestone Gray limestone 3 



11. Grit Sandstone 20 



12. White limestone Light gray limestone 3 



13. Hard grit ditto Sandstone 40 



14. Gray limestone Gray limestone 3 



The Grum is of a peculiar character, having rather the appearance of a 



conglomeratic, mechanical deposit, than the homogeneous composition usually 

 prevalent in limestone rocks. The white bed (12.) is reckoned superior as 

 a flux for the ironstone to any other in the country. The gray limestone (14.) 

 is noted for forming a cement which hardens well under water. The average 

 specific gravity of this stone is about 2-685. 



The organic remains of this carboniferous limestone are neither so nu- 

 merous nor so well preserved as those of the Wenlock rocks. This may be 

 partly owing to the difference of mineralogical composition between the two 

 formations. In the older deposit, the pure carbonate of lime of which it con- 

 sists, has infiltrated into the minutest pores of the fossils ; whilst at Steeraways 

 and Lilleshall the great admixture of silica and alumina has given an earthy 

 texture to all the organic remains. The fossils differ also considerably in 

 their distribution. At Steeraways the Leptana (Producta) gigantea, and Li- 

 thostrotion Jlorlforme of Fleming, are abundant ; while at Lilleshall, Cri- 

 noidea and Cyathophyllum are the most common ; but Leptana hemispherica 

 is especially characteristic of the "^grum."* 



* For the age of this formation see the conclusion of the paper. 

 VOL. V. SECOND SERIES. 3 K 



