Vol. es.] 



AND COKALLIAX ROCKS OF BRILL. 



35 



Cardioceras (Amoeboccras) alter- 



nans (von Bucb). 

 Cardioceras excavatum (Sow.). 

 Belemnites nitidus, Dollf. (with 



phragmocone). 



Cerithium? (very young). 

 Pseudomelania ? (very young). 



Area sp. 



Astarte ovata, Smith. 

 Astarte nionsbeliardensis (?) 

 Contejean. 



Astarte cf. pidla, Roemer. 

 Astarte, two otber species. 

 Ci/prina cyreniformis (?) Blake. 

 Lima sp. 



Modiola bipartite/,, Sow. 

 Ostrea deltoidea, Sow. 

 Ostrea cf. dubiensis, Contejean. 

 Protocardia sp. 



Serpula tetragona, Sow. non, 

 Ream. 



The serpulas are so abundant throughout the rock and so inex- 

 tricable from it, that it is difficult to ascertain to what they can 

 have been attached. In the weathered blocks already mentioned, 

 they were attached to oysters and belemnites ; while oysters in turn 

 had grown upon serpula?. The abundance of Sei-pida tetragona and 

 Cyprina is a point of resemblance to the large doggers described 

 by J. P. Blake 1 from the Lower Kimeridge Clay of Woodhall Spa 

 and Leavening, although the other fossils are not the same. 



When I first visited this section in 1899, only the selenitic clay, 

 a, very little of the overlying clay with phosphatic nodules, and these 

 serpulite-doggers were to be seen. The brickfield comes upon the 

 mapped outcrop of ' Lower Calcareous Grit,' here described as 

 represented by a clay with abundant Ostrea sandalina (Eceogyra 

 nana). I fully expected, therefore, to find Ampthill Clay, and at 

 first the evidence was all in favour of the selenitic clay being 

 Ampthill Clay. Its intensely-selenitic character, the occurrence of 

 phosphatic nodules at the base of the overlying clay, the association 

 of Gryphcea dilatata with Ostrea deltoid ea, and of Belemnites 

 abbreviatus with B. nitidus, are all points of agreement with the 

 Ampthill Clay of Lincolnshire, as described by T. Roberts. 2 In the 

 course of time, however, evidence to the contrary has accumulated. 

 jSone of the species found are exclusively Corallian, while the 

 ammonite Cardioceras altemans (von Buch) is the zone-fossil of 

 the Lower Kimeridgian. It is true that this ammonite has been 

 recorded from the Upper Calcareous Grit of Yorkshire, but that may 

 rather be a reason for including that formation, or part of it, in the 

 Kimeridgian, than for admitting C. altemans as a Corallian fossil. 

 It has, at any rate, never been recorded from the Ampthill Clay. 

 Decisive evidence was provided by the two species of Trigonia — 

 Tr. Juddiana and Tr. Voltzii (the latter, though only a fragment, 

 showing the characteristic feature of growth-lines crossing the 

 tubercles), both species exclusively Kimeridgian. As Tr. Juddiana 

 came from 6 feet below the floor of the pit, we may safely say that 

 nothing lower than Kimeridge Clay is exposed on Rid's Hill. 



The thickness of the Upper Kimeridge Clay here may be estimated 

 at 50 feet, and that of the Lower Kimeridge Clay at not less than 

 the same amount. 



If all the clay exposed in the brickfield is Lower Kimeridge Clay, 



1 Quart. Journ. Geol. Soc. vol. xxxi (1875) p. 210. 



2 Ibid. vol. xlv (1889) pp. 550 et seqq. 



d2 



