Vol. 69.] IN THE MAGNESIAN LIMESTONE AT HARTLEPOOL. 



205 



lying round the wells, but no fossils could be detected in tbem. 

 The limestone is similar in appearance to the flaggy beds which 

 underlie the Uppermost Limestones in the Hesleden-Dene section. 

 It is a well-bedded brown and grey fissile rock of extreme hardness, 

 containing nearly 43 per cent, of a fine siliceous residue. 



(3 a) Blackball Rocks. 



This is the only spot on the Durham coast where the true Shell- 

 Limestone is exposed in the shore-section. The Shell-Limestone 

 reef occurs only a short distance inland all the way down the 

 •coast from Sunderland to Hesleden Dene ; but the actual exposures 

 of rock on the shore are either the Upper Limestones or the 

 unf ossiferous breccias which occupy the eastern flank of the 

 Shell-Limestone. The section is as follows : — 



Upper 



Limestones. 



Thickness 



in feet. 



Dusty, porous, decayed lime-^| 

 stones. Generally well-bedded ! 

 and occasionally massive. I 

 Much collapsed. Hollow \ 

 pseudomorpliic aggregates after | 

 sulphates plentiful in places ... J 



Peastone in part of the section ... 



Upper Shell-Limestone with inter- "^ 

 stratified conglomerates. Large 

 and small irregular rounded 

 masses of variable hardness. 

 In parts apparently piled to- 

 gether indiscriminately, in other 

 parts in distinctly stratified 

 order. Several bands of bedded 

 limestone appear between the 

 layers of rounded fragments. 

 Hard limestone showing much 

 internal deformation J 



Ease not seen. 



60 No fossils 



Dwarfed and impoverished 

 Shell-Limestone fauna. 1 



A band of small gasteropoda 

 and other forms occurs 

 locally about the middle of 

 the conglomerate. 



1 Lists of these fossils are given in tabular form in § VII, p. 215. 



The Middle Limestones are here exposed over a length of slightly 

 under a mile of coast-line. Both north and south of this section 

 the Upper Limestones are faulted down against the Middle Lime- 

 stones, the incoming beds being in each case the Concretionary 

 Series. 



The well-known caves at this place are due to the rounded 

 masses of Shell-Limestone Conglomerate becoming detached by the 

 action of the sea, and leaving the overlying bedded limestones as a 

 roof to the caves. 



Southwards, the overlying beds occupy the cliff-section until 

 the fault at Cross Gill is reached ; but they change considerably 



