Cotefield Close and Sheraton, Co. Durham. 167 



brought about by causes that liave operated later. 1 At Raisby Hill 

 Quarry, near Trimdon, a few miles to the west, these dolomitic and 

 calcareous rocks are Well exposed in a face 100 to 180 feet high. 2 At 

 the quarry the highly magnesian rocks are called " Basic Dolomite or 

 Crusher Stone ", and the purer rocks are called " Bluestones ". 3 The 

 grey limestones are often fossiliferous. Although no fossils were 

 found in the cores, yet at Raisby Hill they yield fossils, and further 

 west at East Thickley a bed 10 feet in thickness yields a well- 

 preserved and fairly rich fauna of the Lower Limestone. The 

 borings confirm the discontinuous and lenticular nature of these 

 calcareous beds, which Dr. Trechmann has noticed in connection with 

 the field exposures. 



[In the Sheraton boring the limestone became more impure and 

 passed down into the Marl Slate (1 foot thick), beneath which the 

 yellow sands (o\ feet) occurred. The former bed was hard and compact, 

 and beneath it was, as is frequently the case, a band of grey 

 calcareous limestone. No fish-remains were noted in the samples 

 brought up. The Yellow Sands formed the base of the Permian 

 series. At the surface outcrops along the escarpment this consists of 

 a bed of incoherent rounded grains, plentifully stained with iron 

 oxide and irregularly bedded. In its original unweathered condition 

 the bed is here a solid rock with a remarkable quantity of iron 

 pyrites disseminated through it. The upper layers at Sheraton are 

 noticeable for the quantity of other fragments of rock embedded in 

 the matrix of rounded quartz grains. Among these pieces of 

 Carboniferous crinoidal limestone, fragments of chert and bits of grey 

 sandstone occur. A similar rock is recorded from Blackball Sinking, 

 but such fragments do not occur in the north of the county nor along 

 the escarpment. 4 — C. T. T.] 



The decrease in the thickness of the Yellow Sands at Blackhall 



1 e.g. the thick irregular coarse dolomitic breccias occurring in the 

 calcareous limestone of Eaisby Hill Quarry. 



2 The section of the Lower Limestone at Kaisby Hill is :— Feet. 



Soft Dolomite . . . . . . . . ) caga 



" Crusher Stone " (hard and pure dolomite, 10-40 feet) j 



" Mixed blue " (dolomitic limestone) .... 0-28 



" Bluestone " (highly calcareous rock) .... 28-54 



Dolomite ......... 10 



Marl Slate 1 



Top of Yellow Sands. 

 A coarse irregular dolomitic breccia occurs in the " Bluestone ". 



3 The following analyses of these rocks have been forwarded to me by 

 T. A. Saint, B.Sc, assistant quarry manager : — 



Basic Dolomite (" Crusher Stone "). Bluestone. 



CaCOs 98-75 



MgCOg . . . . -77 



Silica . . . . . -54 



Alumina and peroxide of iron • 30 



100-36 

 100-00 

 4 [In an arenaceous limestone at the base of the Lower Limestone on 

 Tynemouth Cliff, stems of Carboniferous Limestone crinoids occur.] 



