T1IK CAMIMMAN SYSTEM '.:. 



Anh'imes of North-west France both tin- Irish species of 01- 

 occur in the slates of Fumay which umlrrlii- 

 beds of Tremadoc age. Oldhamia radiata has 

 also been found in Belgium, and another species 

 (0. occidens) has been obtained from the Upper 

 Cambrian of North America. 



In further confirmation of this determina- 

 tion of age it has been ascertained that the ^^^^ 

 supposed unconformity between the Arenig 

 Beds and the underlying rocks in Ireland is of 

 an illusory character. The beds formerly re- 

 garded as conglomerates in Wexford have proved 

 to be crush-breccias, and elsewhere the junction 

 beds of the two series are so plicated into one 

 another that it is impossible to find a dividing 

 line, and so far as Messrs. Egan and M'Henry 

 could ascertain in their revision of 1898, 20 

 there is no evidence of any stratigraphical break 

 between them. Jl 



One of the best sections of these Cambrian 

 rocks is that exhibited in the cliffs of Bray 

 Head near Dublin, whence they are sometimes 

 called the Bray Head Series. At the northern _ 

 end of this cliff section are red, purple, and ^1 

 green slates and grits, succeeded on the south 

 by alternating grits and shales. The beds are 

 bent into numerous sharp folds, so that the 

 real thickness is much less than appears at tirst 

 sight. Jukes and Du Noyer estimated the 

 exposed succession at between 3000 and 4000 

 feet, but neither the base nor summit is actually 

 visible These rocks are also well exposed on 

 the coast of Howth, east of Dublin, where they 

 include some remarkable breccias. 



No fossils have been found in these beds 

 except the two or three species of Oldhamia, 

 the trumpet -shaped worm - tubes known as 

 Histioderma, and some spherical bodies with 

 radiating spines which may be Radiolaria. 

 The nature of the markings called Oldhamia 

 has not been definitely ascertained ; Professor 

 Sollas has pointed out that those of 0. radiata 

 are grooves and may have been made by the anterior end of a 

 worm, but those of 0. antiqua are ridges on the upjor tor- 



