MULLION ISLAND. 37 



mud was deposited which ultimately consolidated into shale. 

 Then after a time the ocean becomes again free of mud and the 

 Radiolarian ooze is formed, to be followed by another period of 

 mud deposits and so on. 



But if the Radiolarian chert of MuUion Island was once 

 Eadiolarian ooze deposited on the floor of an ocean hundreds 

 of miles from shore, it follows that at least the whole "West of 

 England must have been at one time the floor of an ocean 

 covered with Radiolarian ooze, and that wherever rocks of that 

 period are exposed there one should find this chert. The main- 

 land of Cornwall should, therefore, have this chert exposed as 

 well as the Island of Mullion. This is now proved to be the 

 case. Messrs. Teall and Lapworth visited us last Easter, and I was 

 privileged to accompany them. We succeeded in discovering 

 these cherts extending for over 800 yards in the cliffs and in 

 the foreshore north of Porthalla. Other extensive exposures 

 have since been traced in Veryan, Caerhays, Grorran, and other 

 parishes, a description of which will appear elsewhere. 



Until Dr. Hinde,* three years ago, described the Radiolaria 

 of the Llandeilo Caradoc Eocks of South Scotland, only a single 

 species of Radiolaria had been noticed from the entire Palaeozoic 

 series, and this was discovered in Saxony. He tells us that "this 

 Scotch chert is the first instance in which, in our area, this 

 description of rock has been traced to the skeletons of other 

 organisms than sponges." 



Thus Mullion Island has the honour of being the second 

 locality in the United Kingdom where Radiolarian chert has 

 been discovered in early palaeozoic rocks, and so far is the only 

 locality in Cornwall where Radiolarian chert is found, in situ, to 

 contain Radiolaria in sufficient state of preservation to enable 

 experts to determine their respective species. 



You may ask at what precise period of the earth's history 

 did these radiolaria live, to what geological system do these 

 cherts belong? That can only be answered by finding some 

 typical fossils in the shales associated with them. Dr. Hicks 

 expects they will prove to belong to the base of the Ordovician 

 system. Only one fossil has been as yet found in the Mullion 



* Annals and Mag. of Natural History, July, 1890, pp. 40 — 59. 



