Vol. 6S.^ SUCCESSION IN THE NORXH-AVEST OF EXGL.VXD. 479 



(7i 10) The Chonetes-a,ii. comoides and 

 Cyrtina-septosa Band. 



This band forms a well-marked horizon, a few feet thick, at or 

 near the summit of the sub-zone. In the type districts it consists 

 of a thin bed of very pure platy limestone, which lies about 

 15 or 20 feet below the base of the lowest Yoredale sandstone. 

 It is everywhere characterized by the abundance of Chonetes aff. 

 comoides, associated with Cijrtina septosa and a small form of 

 Productus striatus. 



The form of Chonetes afF. comoides so characteristic of this band 

 appears to be identical with that figured by Dr. Yaughan^; it 

 does not differ essentially from Sowerby's type, except that the shell 

 is, as a rule, less thickened. In the Western Districts the band is 

 of a pale buff colour, is usually slightly dolomitic, and contains 

 abundant remains of Cyrtina se]ptosa. The band is associated with 

 beds of ' pseudo-breccia,' and underlies a compact nodular bed the 

 surface of which is covered with stick-like concretions, a bed that 

 occurs at this horizon over the whole of the Morecambe-Bay area 

 <P1. XLYI, fig. 2, facing p. 518). 



Geographical distribution. — The band is shown by a 

 special symbol on the accompanying maps (Pis. LIIl-LY). It 

 occurs in most of the districts where the highest layers of the 

 Lower Dihunojyhyllum Sub-zone are exposed, notably on the dip- 

 slopes at Grandy and on Gathorn Plain in the Shap District ; 

 along the coast in the neighbourhood of Jenny Brown's Point 

 in the Arnside District; on Grange shore. Holm Island, and at 

 Humphrey Head in the Grange District; also in Little Urswick 

 Quarries and along the coast-line in the Purness District. The 

 band is not distinctly marked in the Westmorland Pennines ; but 

 a similar layer, separated by some 40 feet of rock from the base 

 of the Upper Dihunopliyllum Sub-zone, occurs in West Yorkshire 

 between Pibble Head and Great Whernside, where the band again 

 appears in the form of a yellow dolomite, and contains casts of large 

 specimens of Cyrtina septosa. The specimens figured by Phillips ^ 

 and Davidson ^ appear to have been collected from this band. 



(i & k) The Upper Dibitnophyllum Sub-zone. 



This sub-zone comprises by far the thickest series of deposits of 

 tlie Lower Carboniferous sequence in the j^orth- Western Province, 

 and marks the return of shallower water ; the conditions, how- 

 ever, differed considerably from those which obtained during the 

 deposition of the Atliyris-glahristria Zone. The same conditions 

 must have prevailed over a large area in Westmorland, Lancashire, 

 €umberland, Durham, Northumberland, and Yorkshire ; and, as in 

 the case of the lower sub-zone, there appears to have been direct 

 connexion also with the South-Western Province, at all events, 

 at the beginning of the period, for LonsdaUa floriformis marks the 



1 Q. J. G. S. vol. Ixi (1905) p. 295 & pi. xxvi, fig. 4. 



2 ' Illustrations of the Geology of Yorkshire ' vol. ii (1836) pi. xi, fig. 7. 



' Moiiogr. Pal. Soc. ' Brit. Foss. Brachiopoda ' vol. ii (1858-63) pi. xiv, fig. 8. 



