236 MISS G. E. WATXEY AND MISS E. G. WELCH OX THE [Ma}' 191 1 , 



graptolites by the marked dorsal curvature conspicuous throughout 

 its length. 



Locality, etc. — Wan dale Hill, zone of M, nilssoni ; associated 

 with M. boJiemicus, M. nilssoni, and 31. colonas. 



In conclusion, we wish to express our gratitude to Dr. Marr 

 for all the advice and encouragement which he has given us 

 throughout. We also wish to thank Prof. Charles Lapworth for 

 the interest which he has showu in our work ; Mrs. Shakespear 

 for help in the identification of fossils and for the drawings of 

 the graptolites figured in this paper ; and Miss G. L. Elles, D.Sc, 

 for much help in the past. 



EXPLANATION OF PLATE XII. 



Geological map of the Cautley aud Kavenstonedale area, 

 on the scale of 3 inches to the mile, or 1 : 21,120. 



DlSCTTSSIOX. 



Prof. T. McKjenny Hughes thought that the Fellows of the 

 Society would be best able to realize the difficulties with which the 

 Authors had been confronted, if they were to imagine that the 

 Eastern Counties had been upheaved some 2000 feet, and that deep 

 valleys and bays and inlets had been cut through the newer rocks, 

 exposing the floor of older rocks below, which had been folded and 

 faulted and altered ; and that the parts under observation consisted 

 of rocks differing little in detail of lithological character through 

 great thicknesses, while fossils were scarce and badly preserved. 

 Such represented very fairly the problem which the Authors had 

 attempted to solve when they undertook to determine the sequence 

 and distinguish the zones in the Silurian rocks exposed by denu- 

 dation in the deep valleys cut through the Carboniferous rocks of 

 West Yorkshire. 



Edward Forbes had explained the importance of taking repre- 

 sentative forms in classifying strata by their fossil contents, 

 pointing out that percentages of fossils in common did not furnish 

 a basis for correlation, unless the forms were identical or repre- 

 sentative — that was, if nothing but trilobites had been found in 

 the one, and nothing but brachiopods in the other, and there were 

 not a species in common, still the beds might not be remote in age. 

 The Authors, as might be seen in their tabular synopsis, had recog- 

 nized the importance of this as far as was possible in the circum- 

 stances, and had taken various species of graptolites as charac- 

 teristic of zones. It was obviously not a pedigree, and it remained 

 to be found out where the variations arose and why new forms took 

 the place of the old. Here again the speaker wished to call atten- 

 tion to the difficulties of the work. Graptolites were hard to find, 

 especially when the beds had been cleaved and altered, and the 

 sheen of rain was on the rock. 



