32 



3. The Distribution of the Rhabdophora. 



I have reserved for separate treatment one of the most 

 illuminating papers ever published, that ' On the Geological 

 Distribution of the Rhabdophora' (18). This, Lap worth tells us, was 

 partly written in 1873 as a sequel to that on Classification (6), but 

 was not published till 1879 m order that he might be able to visit 

 many of the most important graptolite-bearing regions in the 

 country and to study specimens sent to him from South Wales, 

 County Down, and elsewhere, in addition to those of Scotland. 

 From the paper itself it is clear that he visited and studied 

 carefully not less than thirteen of the localities with which he deals, 

 places as far apart as Pomeroy and Shropshire, Llandeilo and 

 Lakeland. 



After discussing classification and difficulties, and passing in 

 review the earlier and later history of the subject, the Author 

 under the head of ' Data ' deals with the graptolites found in 

 each Formation from the Tremadoc up to the Ludlow, separate 

 zones being recognised where possible or desirable. Then follows 

 a series of range-tables for all known forms to show the distribution 

 of species within each Formation, and a single table for all 

 known genera and species of British Rhabdophora. Next comes 

 an account of each family and genus in relation to its range and 

 peculiarities. Finally there is a list of graptolite zones so far 

 established, and the distribution of graptolite genera within them, 

 closing with an account and a most illuminating table of the dis- 

 tribution of known zones over the British Isles, Europe, and 

 America. 



Two important general conclusions formulated in this paper 

 are quoted below : 



*" The host of proofs formerly supposed to be afforded by the 

 abnormalities of the vertical distribution of the Graptolithina, in 

 favour of the doctrine of migration and colonies, vanish into thin 



air We have at present no evidence whatever to show 



that any single Graptolite group, or even a single species or variety, 

 made its appearance at an earlier date in one region than in another ; 

 and, as a consequence, the place of its origin and the direction of 

 its extension in space are at present equally incapable of recog- 

 nition." 



*" All these circumstances conspire to render the Graptolite 

 one of the most suitable of fossils for the purposes of the working 

 geologist and systematist ; its short vertical range affording 

 elements for the sub-division of the accepted Lower Palaeozoic 

 formations into their component zones ; its wide horizontal dis- 

 tribution allowing of the exact parallelism of synchronous deposits 



* 18, p. in (of separate). 



