The Carboniferous Limestone of West Cumberland. 81 



Limestone developes in places into a sandstone, 6 to 10 feet thick, 

 with numerous plant-impressions. On a weathered surface the 

 sand-grains stand out as brown lines, and give the rock a striking 

 appearance. The walls on either side of the Eowrah to Kirkland 

 road are built of this limestone and show up the diagonal bedding 

 to perfection. This feature, when present, distinguishes the Seventh 

 or Bottom Limestone, being absent from all the other limestones. 



The Fourth Limestone. — The Fourth Limestone (Tab. Ill) can be 

 subdivided into several distinct beds, and the intercalated mud- 

 stones, shales, and sandstones are persistent over an area extending 

 beyond the limits of the district under consideration. This 

 limestone, which is highly fossiliferous throughout its thickness, 

 affords the best exposures throughout the district, and is the one 

 most frequently quarried ; indeed, at present (1921) no quarry is 

 being worked in any other limestone. The thicknesses usually given 

 in vertical sections are 256 feet in thevicinity of Glints and 312 feet at 

 Yeathouse, but by direct measurement the thicknesses are slightly less. 

 The best exposures are at Kelton Head and Rowrah Head, where 

 the full sequence can be seen and studied. Other good exposures, 

 but lacking some of the top beds and their connexion with the 

 Third Limestone, are at Rowrah Hall, Salter Hall, Postlethwaite's 

 Eskett. Yeathouse, and Glints Quarries. The junction of the 

 Di" with the D.^-subzone occurs about 50 feet above the base of this 

 limestone ; it is distinguished by a thin calcite-mudstone lying 

 between shales with plant-impressions. The calcite-mudstone 

 contains Spirorhis-\\kQ annelids, small gastropods, beside Girvanella 

 sp. and similar algae. Girvanella sp. also occurs encrusting -small 

 fossils and crinoid-fragments in the limestone immediately above 

 the ealcite-mudstone. 



The Fourth Limestoke. 

 Table III.— Lithology. 



Thickness. S.W. N.E, 

 ft. ft. 



Black Chert Beds . Dark blue-grey limestone with chert 

 nodules along bedding ; middle bed 

 calcite-mudstone ... 10 15 



Shale . . . Mottled mudstone, with concretions . 1 2 



Junceum Beds . . Thick-bedded blue-grey limestone with 



platy crinoidal band towards top. 

 Chert (Kelton Head). Little shale 

 along bedding planes which are 

 usually concretionary towards toj) 

 but absent in massive lower 

 portion , .... 55 65 



Saccammina Beds . Greenish-grey limestone separated from 

 above by 1-2 feet of mottled shale 

 or mudstone . . . . 18 25 



Upper Algal (?) Band. Micaceous sandstone (Glints); 



nodular and porcellanous limestone 2 5 



Pot-holes Bed . . Thicli post of light-grey limestone 



without shale partings. Pot-holes 

 abundant and persistent. 



VOL. LIX. — NO. II. 6 



