﻿Ixxxii 



PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I905, 



fossiliferous beds of those slates to this age, although even there 

 some of the fossils may belong to rocks of earlier and later date. 



Unfortunately, we are even now unable to indicate the exact 

 position of the base of the division, for we do not know how far 

 beds which have been assigned to it are contemporaneous with the 

 higher Tremadocian strata of the Cambrian system. (I follow 

 British writers in retaining the Tremadocian rocks in the Cambrian 

 system, though many Continental geologists place them with the 

 rocks referable to the Ordovician system, for I see no reason to 

 depart from the classification which was originally applied.) 



The graptolitic beds of Skiddavian age have been satisfactorily 

 grouped, and I here reproduce the table drawn up by the latest 

 worker on these beds in Britain, namely, Miss Gr. L. Elles, 1 merely 

 substitutiug the name ' Skiddavian ' for ' Arenig Series,' which 

 appears in Miss Elles's paper : — 



Walks. 



Shropshire. 



Lake-District. 



Scania. 



■ 





( 



i 



Zone of 

 Qlossograptus. 



Zone of 



Lower Hope 



Bllergill Beds. { 



Zone of 



Didymograpius 



Shales. 



| 



Phyllograptus, cf. 



bifid us. 





I 



typus. 



Zone of 



Upper N , 





Zone of 



Didymograpius 



Mytton Flags. | 





Isograptus 



kirundo. 



! 



Upper 



gibberidus. 





y 



Tetragraptus- 





Zone of 



Shelve 



Beds. 





Didymograptus, 



Church Beds, j 



' 





extensus. 



] 

 J 











( 



Zone of 

 Phyllograptus 



? 



Lower Mytton 



\ Dichograptus- J 

 Beds. } 



densus. 





Flags. 



Zone of 







1 



Didymograptus 







i 



balthicus. 



Garth Grit ? 



Stiper Stones 



Lower 



Zone of 





Quartzite. 



I Tetragraptus- 



letragraptus 







l Beds. 



phyllograpioides. 



The beds tabulated above may, then, be taken as defining the 

 upper and lower limits of the Skiddavian Series so far as the areas 

 mentioned are concerned, and it only remains to correlate the 

 Skiddavian Beds of other areas with these. It is especially impor- 

 tant that we should discover what non-graptolitic beds are their 

 equivalents, for, as is well known, it was maintained by the late 



1 ' Some Graptolite-Zones in the Arenig Rocks of Wales ' Geol. 

 1904, p. 199. 



Mag. 



