Vol. 70.] OF DURHAM MAGXESIAX LIMESTONES. 241 



XXXI. XXXII. XXXIII. XXXIV. XXXV. XXXVI. 



Insoluble residue . 0'20 0*08 1-14 2*28 1-92 0*50 



Fe.,0 3 ,etc 0-28 0-13 0-69 I'll 1-04 0-34 



Mn0 0-21 



CaCO, 55-86 96*64 53'69 71-60 53-80 91-92 



MgC0 3 44-54 3-39 44-71 25-42 43-39 8'13 



S0 3 016 0-29 tr. 0-34 tr. tr. 



Totals ... 101-04 100-53 100-23 100-96 100-15 100-89 



Calcite 2-83 92-61 0-46 41-34 2-14 82-25 



Dolomite 97*57 7'42 97"94 55'68 95*05 17'80 



Calcareous Shell-Limestones (Tunstall and Beacon Hills). 



The upper part of Tunstall Hill at the southern end consists 

 of a brown, coarsely-crystalline, calcareous rock. From a part of 

 the hill now largely quarried away, Kirkby obtained a rich and 

 beautiful series of fossils. 1 The rock occurs in large irregular 

 masses, and changes through partial decalcification into a dark- 

 brown, friable, powdery material, enclosing cavities lined with a 

 white mineral allied to ankerite. This material shows much 

 internal deformation, and the decalcification is accompanied by 

 progressive obliteration of the fossils. 



Irregular patches and vein-like masses of a similar brown cal- 

 careous Shell- Limestone occur in the knoll of Beacon Hill, but 

 the rock is more largely altered by decalcification. In both places 

 the rock occasionally assumes a radiating concretionary structure, 

 and is intimately associated with the dolomitic Shell-Limestone. 

 It weathers in small fragments very differently from the dolomite. 



Tunstall Hill. — XXXVII. Hard brown crystalline rock- 

 Full of bryozoa and other fossils. The larger fossils are formed of 

 brown calcite, the smaller of a loose brown manganiferous powder. 



XXXVIII. Brown, partly decalcified material. Fossils obliterated. 



XXXIX is closety associated with XXXVII. A very hard, white, 

 dense Shell-Limestone dolomite, retaining little trace of fossils. 



Beacon Hill. — XL. Dark-brown Shell-Limestone. It is 

 partly decalcified, and the fossils are largely obliterated. 



XXXVII. XXXVIII. XXXIX. XL. 



Insoluble residue 0*10 0-19 0-24 0'28 



Fe o 3 , etc 0*12 0*53 0-63 0*79 



Mn0 o 0*66 6-47 5*88 



CaCO, 98*08 91*17 55*02 89*24 



MgC0 3 1*52 1*80 44*01 4-11 



SO, tr. tr. 0*33 0*18 



Totals 100*48 100*16 100*23 100*48 



Calcite 96*27 89*03 2*62 84*35 



Dolomite 3*33 3-94 96-41 9-00 



1 Now in the Newcastle Museum. The late Mr. J. W. Kirkby considered 

 Tunstall Hill the richest locality in England for the Permian gasteropoda. 



