Vol. 69.] IN THE MAGNESIAS LIMESTONE AT HARTLEPOOL. 299 



There is apparently in Hesleclen Dene a perfectly conformable 

 passage, down from the Uppermost White Limestones to the Upper 

 Shell- Limestone, without any trace of development of concretionary 

 structure. Neither the typical fossils nor any trace of Filograna 

 occur in the presumed equivalents of the Concretionary Series. 

 The same applies to the Hard wick-Dene section. 



The Shell-Limestones are exposed for a distance of over a mile, 

 coming in at Jackdaw Rock, at which point the overlying yellow 

 fissile limestones dip sharply south-westwards at an angle of 

 about 15°, and ending with the disappearance of the rock beneath 

 Boulder Clay at the top of the dene. 



Overlying and partly replacing the Shell-Limestones is a series 

 of soft, white, bedded limestones, very porous and friable, but 

 occasionally massive, with dusty cavities arranged along the planes 

 of bedding. They are often full of hollow cavities, presumably 

 pseudomorphic after sulphates. These beds are excessively tumbled 

 and collapsed in part, with development of calcareous ribs and 

 irregular segregated breccias. 



From the nature of the fauna as well as from their position, the 

 beds at the upper end of Hesleden Dene are regarded as the highest 

 Shell-Limestone that occurs in the county of Durham. 



(5) Castle-Eden Dene. 



This is a ravine extending in a north-easterly and south-westerly 

 direction for a distance of nearly 5 miles. The valley is of pre- 

 Glacial origin, and upon the Boulder Clay that fills the pre-Glacial 

 wash-out the present stream has been superimposed. The stream 

 apparently coincides with the line of the pre-Glacial wash-out in 

 only the last part of its course, and empties itself into the sea near 

 the northern boundary of the original valley, which has a width of 

 about a third of a mile. 



The result is that the stream has in places cut a very deep gorge 

 into the rock, exposing a fine and nearly continuous section in the 

 Middle Magnesiau Limestones for a distance of over 3 miles. 



The strata in the shore-section at the mouth of the dene, as 

 already described, belong to the Uppermost Limestones, and are here 

 probably faulted down against the bank of Shell-Limestone. 



The following section of Shell-Limestone is exposed near the 

 entrance of the dene, between Deneholme and the railway-viaduct, 

 in the bed and on the southern bank of the stream : — 



Thickness in feet. Fauna. 



"Grey and yellow, crystalline, tine- ~1 

 grained limestones of variable 



hardness, passing locally into fA highly bryozoonal lime- 



breccias of varying degree of I stone, with plentiful ostra- 



fineness, in which irregular ! „q J cods. 



pockets and masses of powdery [ " \ Rock largely made up of 

 material occur. I I comminuted fragments of 



Fossils in all stages of preserva- [_ various organisms, 



tion, from perfect preservation I 



„ to complete obliteration J 



The Shell-Limestone is again finely exposed between the Garden - 

 of-Eden Bridge and White Bock. 



Upper 

 Shell- 

 Limestone. 



