Yol. 68.] SUCCESSION IN THE NORTH-WEST OF ENGLAND. 459 



PI or a. — Calcareous algse occur abundantly at two levels : 

 namely, at the base of the lower and of the upper sub-zones re- 

 spectively ; while ArclmosigilJaria vanuxemi is apparently confined 

 to this zone, but occurs at more than one level. 



Pa una.— The fauna of this zone is, on the whole, a very 

 distinctive one, and it is doubtful whether any of the forms pass 

 up beyond the base of the overlying Michelinia Zone. The detailed 

 account of the fauna will be best considered under the different 

 subdivisions. 



Geographical distribution. — This zone occurs in all the 

 districts, but its full development is only found in the Shap and 

 Ravenstondale Districts, where it attains its maximum thickness 

 of 1335 feet. Elsewhere, as in the Westmorland Pennines, 

 submergence took xDlace at a somewhat later period, and only the 

 upper portion of the zone is there represented. The zone may be 

 divided into two sub-zones, which contain altogether six palseonto- 

 logical horizons or ' bands ' : — 



Sub-zones. Bands. 



({Q>) The S'pirifer-furcatus Band, 



(5) The Brownber Pebble-Bed {8yri)i 



I thyris-cuspidata Band). 



{b) Semmula-ffregaria Sub-zone ...{ (4) The Thysanojpliyllum-jpseudovermicu- 



lare Band. 



I (3) The Productus-glohosus Band (with 



1^ an algal layer at the base). 



. . _, ^ ^ - f (2) The Camarotoechia-2oroava Band, 



(a) SolenoporaSxCo-zoTiQ | ^^^^ r^^^^ Vat^yhania-cleistoporoides Bemd. 



(a) The Solenopora Sub-zone. 



In this sub-zone are included all the beds from the base of 

 the Shap Conglomerate to the base of the Productus-glohosus Band. 

 In the Shap District about 100 feet of beds may be assigned to 

 this sub-zone, while in the Kavenstonedale District it reaches its 

 maximum thickness of 1020 feet. The two districts are directly^ 

 continuous, the lowest bed in each representing approximately the 

 same horizon. This difference in thickness is due to the thinning 

 of the individual beds Avhen traced northwards, and not to any 

 appreciable overlap of the upper beds on to the under- 

 lying Lower Palseozoic rocks. The interesting calcareous alga 

 Solenopora has been selected as the index-fossil, on account of its 

 presence throughout the sub-zone and its wide lateral distribution 

 (PL XLYII, fig. 1). It has not been met with above the base of 

 the Productus-glohosus Band, but is found wherever the lower beds 

 of the Athyris-glahristria Zone are developed in the ISTorth- Western 

 Province. This organism has not previously been reported from 

 the Upper Palaeozoic rocks ; indeed, it was hitherto known only 

 from beds of Ordovician and Jurassic age. Its discovery in the 

 Lower Carboniferous rocks of Westmorland, therefore, will assist 



