190 Mr. C. Lapworth on the Geological 



The novelty and complexity of the subject constitute a 

 sufficient apology for the multiplicity of the evidences brought 

 forward in the earlier portion of this paper, and for the detailed 

 indication of the several results that may safely be deduced 

 therefrom. The widespread disbelief in the value of the 

 Graptolite as a geological index is hardly likely to be over- 

 thrown by any thing short of a perfect demonstration of the 

 contrary opinion. I have therefore felt it necessary to adduce 

 all the more important facts and arguments which appear to 

 me to substantiate my views, that the evidences may be 

 weighed collectively and in detail by each student for himself 

 personally, and the way cleared for a new and more correct 

 departure in this regard. 



Our present knowledge of the details of the physical and 

 palaiontological succession of the British Proterozoic rocks is 

 admittedly superficial. Much painstaking and extended re- 

 search is necessary before we shall be prepared to say with 

 confidence what are their most natural subdivisions, and what 

 are their special and peculiar fossils. That some of our rock- 

 formations will be found in future to be of far greater value 

 in the geologic scale than is now admitted is tolerably certain ; 

 but, at present, it is impossible to guess either in what respects 

 our received classification is deficient, or what groups have 

 been ignorantly assigned an exaggerated and unnatural im- 

 portance. 



Nor is the zoological department of our subject less tenta- 

 tive and imperfect. The absence in the fossil Graptolites of 

 those soft parts of the animal which are of such primary 

 importance in the determination of the inter-relationships of 

 their modern allies among the Hydrozoa, forces us to rely 

 exclusively upon elements of classification derived from the 

 less-reliable peculiarities of their hard skeletons. This gives 

 a character of uncertainty to our schemes of arrangement, which 

 is felt most keenly by the graptolithologist, as he is forced 

 to look upon his larger divisions as only doubtfully permanent 

 in their composition and gradation. On the other hand, his 

 smaller groups, which, from his special training are to him 

 more a matter of instinct than of logical demonstration, are 

 less easy of acceptance by the average palaeontologist, who, 

 recognizing the simplicity in structure and close resemblance 

 in externals among all the Rhabdopora, looks upon the 

 minute criteria by which the graptolithologist classifies his 

 families, genera, and species as being frequently trivial in 

 character and not always available in application. 



In all these respects our two scales (the geological and the 

 zoological) are pretty much upon a par. In both we recognize 



