454 PKOF. E. J. GARWOOD OX THE LOWER CARBONIFEROrS [DoC. I912, 



This species is practically confined to the Seminula-gregaria Sub- 

 zone, and, though on the whole a rare shell in the ^^orth- Western 

 Province, it sometimes occurs in fair ahun dance in the Eastern 

 Districts, where it is invariably associated with arenaceous and 

 oolitic deposits, and is especially characteristic of the Brownber 

 Pebble-Bed. In the Western Districts, however, where this horizon 

 is composed of calcareous rocks, it has scarcely ever been met with. 



A further interesting feature which may be cited in this con- 

 nexion, is the association of calcareous algse with lagoon conditions. 

 These organisms flourished only at three horizons in the Xorth- 

 Western Province, namely, in the Solenopora Sub-zone, at and near 

 the base of the Seminula-gregaria Sub-zone, and again at the base 

 of the Upper Dibunoplujllum Sub-zone. In the first two cases the 

 remains of calcareous algae are closely associated with dolomitic 

 deposits ; while, in the last, clear but shallow- water conditions seem 

 to have prevailed, in which masses of Lithosfrotion and Lonsdalia 

 grew somewhat after the manner of modern coral-reefs. 



The most interesting lithological change met with in tracing the 

 different horizons across the area from west to east occurs in the 

 case of the Miclielinia Zone and the beds immediately overlying it. 

 This zone attains its fullest development in the Arnside and other 

 western districts, where it contains one of the richest faunal assem- 

 blages found in the Lower Carboniferous rocks of the Xorth-Western 

 Province. In the Shap District and in the AYestmorland Pennines 

 this zone seemed, at first sight, to be entirely missing, and its 

 apparent absence originally introduced a difficulty in correlating 

 the individual beds of the Eastern with those of the Western 

 Districts. The discovery, however, of Miclielinia granclis in the 

 Camaroplioria-isorliynclia Bed at Shaj) proved conclusively, what had 

 previously been strongly suspected, that the f ossiliferous Michelinia- 

 Beds of Arnside were represented in the Shap District by the 

 almost barren deposits at the base of the Orton-Sandstoue Series ; 

 while the corresponding horizon in the Westmorland Pennines has 

 been found to lie in the oolitic grits and unfossiliferous sandstones 

 underlying the Melmerby-Scar Limestone, along the foot of the 

 Cross-Fell escarpment. This arenaceous deposit, the Orton and 

 Ashfell-Sandstone Series, affords one of the most striking examples 

 of the transgression of a definite lithological facies across a series 

 of faunal lines. (See map, PL LIY.) 



This sandstone episode, which in the Shap District occurs at the 

 base of the Miclielinia Zone, enters at a progressively later period 

 as we travel southwards towards the Eavenstonedale District uutil,^ 

 when we eventually reach the neighbourhood of the Dent Eault, 

 the base of the Ashfell Sandstone is seen to lie some 100 feet above 

 the base of the Lower Procluctus corrvgato-liemisijlieric^is Zone. At 

 the same time, the faunas of both these zones gradually increase in 

 importance as we pass southwards into the region where the sand- 

 stones are gradually replaced by calcareous rocks. ^ 



^ See map and description of the Shap and Eaveustonedale Districts. 



