472 PEOr. E. J. GARWOOD ox THE LOWER CIRBOXIFEROUS [DeC. I912, 



Arnside Knott. This line is rather one of convenience than a strict 

 zonal horizon, since the index-fossil is not found in the lowest 

 compact limestone, Tvhich may indeed in part represent the Cyrtina- 

 carhoiiaria I3eds of the eastern districts. In the western districts 

 the overlying Bryozoa Band is also absent, and the upper limit of 

 the sub-zone is taken at the base of the Lower Dihunoi)liijllum Sub- 

 zone. 



Lit ho logy. — The rocks are always calcareous, and never dolo- 

 mitic. They vary from compact white limestones to thinly-bedded 

 calcareous shales. In the type districts and in the Westmorland 

 Pennines they usually occur as a dark-grey, somewhat argillaceous 

 and thinly-bedded limestone. Round Morecambe Bay the beds are 

 divisible into a lower compact and an upper, thinly-bedded, shaly 

 limestone, crowded with Chonetes iDcipilionacea. In the Eastern 

 Districts that form is practically absent, and the upper shaly 

 Ch.-papilionacea Beds of Arnside Knott and AYhitbarrow must 

 include the horizon of the Bryozoa Band of the Eastern Districts. 

 Where the sub-zone reaches its greatest development on Arnside 

 Knott it cannot be far short of 330 feet in thickness; but, in the 

 Shap District and along the Pennine Escarpment, the sub-zone is 

 reduced to a comparatively thin deposit immediately overlying the 

 Orton and Swindale Beck Sandstones, which probably include a 

 part of this sub-zone, the upper portion only being represented by 

 the lower portion of the Knipe-Scar and Melmerby-Scar Limestones. 



Eauna. — XematopliyUmn minus was described by !M'Coy from 

 specimens collected in the Kendal District. His name has, there- 

 fore, been retained, in order that the exact form characteristic of 

 this sub-zone may be recognized with certainty, although (as pointed 

 out on p. bQ-\i) it is undoubtedly a Lithostrotion, and this species 

 may even be the genotype. The size of the corallites varies con- 

 siderably, being smallest in the Eastern Districts, where siliceous 

 deposits predominated in the lower portion of the sub-zone. In 

 the Western Districts CJionctes papilionacea ^ occurs throughout the 

 sub-zone, and is so abundant in the upper portion as to impart a 

 fissile character to the limestone. So numerous are the individuals 

 of this species that it might well give its name to the sub-zone, 

 were it not that specimens are practically absent from the type 

 districts and from the Pennine Escarpment, while SematopJn/Ihon 

 iiiinus^ as already mentioned, is found throughout. Again, forms 

 w^hich, though smaller, cannot be readily separated from this species 

 of Chonetes, occur in the underlying portion of the zone, and even 

 sparingly in the JlicJielinia Zone below. jS^o other form is confined 

 to this sub-zone, or can be deemed specially characteristic 'of it. 



1 This form is doubtfully referred to Phillips's species. The form alluded tb 

 here is that shown in fig. 5. pi. xlvi vol. ii of Davidson's ' Fossil Brachiopoda ' 

 <Monogr. Pal. Soc.) 1858-63. 



