AT CLAXHF.IIOH AND DOWN HIT,!,, CO. DUTUIAM. 157 



washed down by torrential streams and mainly deposited 

 under continental conditions. The breccias of Cumberland 

 (Whitehaven district) were also deposited on a land surface*, 

 {l>) The fossiliferous breccias at Blackball Rocks are com- 

 posed of blocks that have rolled down the eastern edge of the 

 Reef, /.(?., Vorreeft, (<^) Some of the breccias were produced 

 bv thrusting (crush breccias) e.g., those so well exposed at the 

 south end of Marsden Bay, (d) others may be due to the 

 removal of beds and intercalations of gypsum and anhydrite, 

 as those exposed on the coast of Durham near Easington, 

 (<?) while the breccias at Raisby Hill Quarry appear to 

 have been produced by hard calcareous beds (bluestones) 

 becoming changed into soft cellular dolomite (the magnesia 

 being derived from the dolomite above) and then the layer 

 breaking up. The last three would be associated with 

 disturbance in the strata, the two former would not. 



It is thus clear that the causes of the brecciation and of the 

 disturbed strata in the Magnesian Limestone are many, and 

 that the evidence from each exposure must be carefully 

 examined before an explanation of their mode of formation 

 can be elucidated. 



The disturbances at Claxheugh and Down Hill occur 

 beneath the level at which sulphates were laid down (they 

 aflfect the Yellow Sands, Marl Slate and Lower Limestone) 

 and afford clear proof of having been produced by horizontal 

 movements, and cannot be directly due to the Magnesian 

 Limestone having contained gypsum or anhydrite, nor to the 

 removal of beds of Limestone, Marl Slate and Yellow Sands 

 by solution or underground mechanical action of running 



* Dr. Trechmann and I have lately examined both of these beds and 

 agree as to their mode of formation. 



t In Thuringia a Bryozoa reef occurs in the Lower Zechstein, similar 

 in nature and fossiliferous contents with that of Durham, and a Vorreef is 

 present also. Geologisches Wanderbnch fiir Ostthiiringien und West- 

 sachsen by E. Kirste, page 14 1. Dr. Trechmann and I who examined 

 the Thuringian beds in 19 13 were struck by their resemblance to those of 

 Durham. 



