R. M. Brydone — Stages of the U]jper Chalk. 59 



overlap even that of B. mucronata, and it is very dangerous to base 

 any classification on the assumption that it never overlaps that of 

 A. quadratus. 



The next point to catch my eye is the tabulation of A. verus, 

 A. quadratus, and B. mucronata as having absolutely distinct ranges 

 in Belgium. In a paper by M. Rutot (Bull. Soc. Beige Geol., 

 tome viii, pp. 145-194, 1894) it is strongly emphasized that in 

 a division consisting of pure white chalk and known as the " craie 

 de Trivieres " (and in one case, to judge from a section given, in an 

 exposure of the upper part only of that subdivision) the three 

 Belemnites above mentioned are found associated. Unless this 

 statement has since been verj'- thoroughly disproved it is dangerous 

 to tabulate the ranges of A. verus and B. mucronata as separated by 

 two whole zones. 



The next point for consideration is the statement (previously alluded 

 to) on p. 313 that it is a fact that the highest beds in the Yorkshire 

 cliffs belong to the zone of 0. pilula ; in other words, that there 

 is no chalk of the restricted zone of A. quadratus exposed in the 

 Yorkshire clife. 



Now it is obvious that if this statement ought to be accepted 

 as an unquestioned fact, it cannot have been demonstrated in 

 any earlier publication, and the argument proving it must be 

 sought in Mr. Jukes-Browne's paper ; and it would seem to be 

 an essential element of such an argument that some test should 

 have been established by which the boundary between the zone of 

 0. pilula and the restricted zone of A. quadratus in Yorkshire can 

 be determined and recognized with reasonable certainty. No such 

 argument or test is directly stated, but it appears to be implied that 

 the absence of A. quadratus has been treated as such a test. This 

 is not a test for South England, and even if it has been absolutely 

 demonstrated on the Yorkshire coast — and there is an immense 

 diffei'ence in the case of A. quadratus between "has not been found " 

 and " does not occur " — it remains to be proved that it is a valid and 

 conclusive test for Yorkshire. This leads on to a point which goes to 

 the root of the reliability of many of Mr. Jukes-Browne's instances 

 of fossils which do occur in the zone of 0. pilula but do not occur in 

 the restricted zone of A. quadratics, and which is best explained 

 by a concrete case. Mr. Jukes-Browne cites Inoceramus lobatus as 

 occurring in the zone of 0. pilula, but not in the restricted zone of 

 A. quadratus. This citation must, from his general remarks, be 

 based on statements in Mr. Woods' monograph. There we find 

 I. lohatus recorded only from Yorkshire, but from many places 

 in that county. How can any degree of reliability attach to the 

 statement that this species occurred always below, never above, 

 a line which has not yet been determined ? This consideration 

 would seem to rule out the employment of any specimens recorded 

 from the old zone of A. quadratus in Yorkshire as evidence in 

 establishing a stage break in the middle of that zone. I am afraid 

 it also tends to the conclusion that it is dangerous to employ for 

 that purpose many of the records from the South of England so 

 employed by Mr. Jukes-Browne, although conditions are less 



