G. L. EUes — Graptolite Zones in Arenig JRocks. 199 



as this channel was filled up by the fossiliferous sands and other 

 deposits the coal-bearing series followed under estuarine and fluviatile 

 conditions. Therefore I think that these borings pierce strata 

 inferior to the coal series. 



In some parts of the Caroni and Oropuch country occurs a large 

 estuarine formation which, in my opinion, succeeded the Miocene 

 formation, and was deposited by the Miocene and Pliocene extension 

 just mentioned of the river Guarapiche (see my papers in Geological 

 Society's Journal, 1892; Geological Magazine, 1900; and Pro- 

 ceedings Victoria Institute, Trinidad, 1902). It is a very fine- 

 grained argillaceous formation, frequently capped by fresh-water 

 gravels, and this may very probably overlie the coal series in places. 



Note. — I am informed that at the site of the borings near the 

 Cunapo rivei', about seven miles from Sangregrande, the surface is 

 about 150 feet above sea-level. 



Second Note. — In reference to the conclusions arrived at from 

 this imperfect study of the geology of the Sangregrande district, 

 I may quote a remark by S. A. Miller in his "North American 

 Geology," etc., that " a general knowledge of geology is probably 

 of greater importance to the people of the United States than a like 

 amount of information in any other department of natural science," 

 a remark which might be extended to a larger area than the 

 United States. 



EXPLANATION OF FOLDING PLATE VII. 



Diagrams showing the strata passed through in the Sangregrande Borings 

 Nos. 1, 2, 3. 



[To be continued.) 



II. — Some Graptolite Zones in the Arenig Eocks of Wales. 



By Gektrude L. Elles, Newuhaui College, Cambridge. 



rpHE Arenig Series, as originally defined by Sedgwick, has 

 JL undergone much subsequent modification by its founder and 

 other authors. There have been separated off from it the Tremadoc 

 Series at the base, and the Llandeilo Series above, and a certain 

 amount of ambiguity has arisen as to what constitutes the Arenig 

 thus restricted ; possibly, therefore, the recognition of three well- 

 defined graptolite sub-faunas within the series in certain districts 

 may help in some degree towards the solution of the problem. 



In both North and South Wales there appears to be a well-defined 

 belt of rocks characterised by graptolites of the ' tuning-fork ' type 

 (dependent series). In South Wales this constitutes Hicks' Llanvirn 

 Group ; it comprises two zones — 



1. ZoMQ oi Didymograptiis Murchisoni. 



2. Zone of JDidymograptus bifidus. 



The upper zone of D. Murchisoni is the equivalent of the beds 

 forming the lower part of the Llandeilo Series, including the 

 Llandeilo Limestone, in part at any rate ; the lower zone of D. bifidus 

 is the uppermost limit of the Arenig Series. 



