Vol. 68.] SUCCESSION- IN THE NORTH-WEST OF ENGLAND. 549 



locally at several other horizons, the nuclei of the oolitic granules 

 being frequently quartz-grains. 



Dark bituminous limestones occur universally at the base of the 

 Upper Dihunopliyllum Sub-zone, and are also found in many of 

 the overlying Yoredale limestones. Pure white limestones are 

 limited to the deeper-water deposits of the Nematophyllum-minus 

 and the Lower Dihunojjliyllum Sub-zones. True crinoidal lime- 

 stones are almost entirely absent, with the exception of the thin 

 limestone which occurs in the Upper Bihunopliyllum Sub-zone in 

 the Kirkby Lonsdale District. 



Calcareous mudstones are specially characteristic of the upper 

 portion of the MicJielinia Zone in the Western Districts, where that 

 zone is most fully developed. Thin layers of ' china-stone ' occur 

 locally at two horizons : namely, near the base of the Semimila- 

 gregaria Sub-zone, and in the Bryozoa Band immediately underlying 

 the Bibunojjhyllum Zone. These layers are usually crowded with 

 small spherical bodies, many of which appear to be identical with 

 Qalcispliera fimhriata (Williamson).^ These are invariably asso- 

 ciated with plant-remains at the upper, and with calcareous algae 

 at the lower, horizon. The deposits appear to represent a fine 

 impalpable mud, laid down in the shallow but quiet waters of a 

 lagoon or estuar}-. 



Shales and sandstones are, in most districts, limited to the Yore- 

 dale rocks of the Upper Bibunophyllum Sub-zone. Spotted lime- 

 stones and pseudobreccias are peculiar to the beds of the Lower 

 Dibimopliylliim Sub-zone, and are found in all the districts. The 

 ' spotted ' limestones occur typically at the base and summit of this 

 zone, and appear to represent an incipient attempt at concretionary 

 segregation of the coloured impurities. In a few cases, however, 

 as at Great Eundal Beck in the Pennine District, where this 

 structure is very marked, the spots are due to a definite separation 

 of the calcareous constituents from the detrital sand-grains. The 

 pseudobreccias are practically confined to the upper portion of this 

 sub-zone, and are specially associated with the Clionetes-dM. comoides 

 Band. They appear to owe their origin to the shrinkage of the 

 deposit during consolidation, occasionally accompanied by the same 

 tendency to incipient concretionary action as that which gave rise 

 to the ' spotted ' beds. They would seem to have been deposited 

 under special conditions, involving a general elevation of the 

 sea-floor. 



The lithological conditions which characterize the different 

 horizons are, on the whole, remarkably constant throughout the 

 area ; but three notable exceptions may be mentioned. The first 

 is the important transgression of an arenaceous type of deposit 

 across several of the faunal horizons that occurs in the Shap and 

 Eavenstonedale Districts, traces of which can also be found in the 

 Pennine District on the east and the Kendal District on the west. 

 This sandstone episode, which begins at the base of the MicJielinia 



1 Compare also Sporocarpiis elegans. 



