448 G. T. Prior — Pillow-Lava in Cormcall. 



and near the Methodist Chapel at St. Martin, but at Trethewy 

 the specimen obtained, which was coarsely vesicular, was found 

 loose on a heap of pebbles, and at St. Martin there is some doubt 

 whether the rock was actually in situ. 



Still further west, at Lower Garras ' gravel-pit,' was found a crushed 

 and brecciated radiolarian chert, exactly similar in microscopic 

 characters to that of Mullion Island. 



Boskruge Lane and Higher Boden. — Tn the lane leading from 

 Eoskruge to Higher Boden, on the right-hand side, occurs an 

 andesitic basalt showing large porphyritic felspars. Under the 

 microscope these phenocrysts are seen to occur in a groundmass 

 consisting of a mesh of felspar laths with interstitial dai'k grains 

 of what is probably altered augite. Some yards distant, on the 

 same side of the road, to the east of a small stream, was found 

 a basalt consisting of felspar laths and interstitial brown augite, 

 precisely similar to the Mullion Island rock, but of slightly coarser 

 grain. Similar basalt occurs in a quarry farther up the lane on 

 the left-hand side near Higher Boden. The association of a basalt 

 like that of Mullion Island with a markedly porphyritic variety is 

 repeated on the other side of Falmouth Bay in a quarry near Tubbs 

 Mill (see below). 



Porthallow. — The rock at Porthallow is similar to some of the 

 varieties of basalt found at the quarries near Tubbs Mill on the 

 other side of Falmouth Bay (see below). It shows a trachytic 

 mesh of felspar laths with dark interstitial grains of altered augite, 

 and passes on the margin into a spherulitic glass. 



Nare Head (east side of Falmouth Bay). — On the top of Nare 

 Head was found a basalt consisting, like the Mullion Island rock, 

 of felspar laths and interstitial purplish-brown augite, but containing 

 also a few porphyritic felspars. It was associated with a variety 

 of much coarser grain, approaching a dolerite in character. At 

 Pennare Wallas, north of Nare Head, occurred a radiolarian chert 

 similar to that of Mullion Island. 



Quarries near Tubbs Mill (north of St. Michael Caerhayes). — In 

 a quarry east of Trevennen, on the right-hand side of the road 

 leading to Tubbs Mill, occurs a basalt showing fairly well-marked 

 pillow structure. The rock is like the Mullion Island basalt, and 

 consists of felspar laths and altered interstitial augite. As in the 

 case of the Porthallow rock, it passes on the surface of the pillows 

 into a glass showing well-marked spherulitic structure. In the 

 large quarry just north of Tubbs Mill is seen the close association 

 of a finely vesicular basalt, consisting of felspar laths and pale 

 purplish-brown augite, precisely similar to the Mullion Island rock, 

 with a vai'iety showing a similar groundmass, but with numerous 

 fairly large porphyritic felspars. A similar association of a basalt 

 like the Mullion rock with a porphyritic variety occurs also in an 

 overgrown disused quarr3' amongst osiers to the east of Trevennen 

 on the left-hand side of the road leading to Tubbs Mill. 



Great Ferhaver Beach. — A mass of basalt showing well-marked 

 pillow structure and microscopic characters, similar to those of the 



