and associated peehian eocks or dtjeham. 213 



to the sandstone silica and alumina are its prevailing constituents 

 (Nos. 7, 11, and 12): nearer the limestone carbonates of lime 

 and magnesia form more than five-sixths of its bulk (Nos. 8, 9, 

 and 14. 



It is of no economic value. 



Sub-fokmation.— LOWEK LIMESTONE. 



Geological Characters. — Of various shades of yellow (prevailing 

 tint), brown, grey, and sometimes whitish ; generally compact, 

 often sub-crystalline, occasionally vesicular, rarely friable and 

 tufaceous ; frequently thin-bedded, though ranging from strata 

 an inch thick to others of two feet and upwards, but almost inva- 

 riably well stratified ; fossiliferous in some of its beds. Aggre- 

 gate thickness from two hundred to two hundred and fifty feet. 

 Largely distributed on the western side of the formation. 



]S T o. 16. Locality— SUMMEKHOTTSE, 



TWO MILES N. OF THE TEES. 



Lithological Characters. — A grey, ratter compact and hard, 

 thin-bedded limestone ; fossiliferous. 



ANALYSIS. 



Carbonate of lime 56 - 40 



magnesia 38-88 



Oxide of iron and alumina 0-80 



Sand and clay 1*36 



Water 2-56 



10000 



Forms a moderate road metal ; is also burnt for lime. 



No. 17. Locality— EAST THICKLEY, 



THEEE MILES S.E. OF BISHOP AUCKLAND. 



Lithological Characters. — Smoke grey, compact, and almost 

 sub-crystalline, thin-bedded, with irregular surface planes and 

 partings of yellowish marl ; fossiliferous.* 



* Described by Professor Sedgwick in his Memoir (Trans. Geol. Soc, Ser. II, Vol. Ill 

 p. 76.) as beds No. 3 in the Midderidge and East Thickley section. 



