Q. T. Prior — Pilloic-Lava in Cornicall. 447 



considerable resemblance to those of Diplodocus. The few fragments 

 of centra of the body vertebrae show the peculiar excavations seen 

 in tbe centra of the American types. The best preserved vertebra 

 is the one figured. It is probably one of the posterior dorsals. 

 The spine shows a complicated arrangement of laminse very similar 

 to that of the spines of the posterior dorsals of Diplodocus, but 

 owing to the condition of the specimen it is difficult to represent 

 this in the figure. The height of the vertebra, when complete, 

 would probably be about 450 mm., or less than half the size of 

 the last dorsal of Diplodocus. 



I propose to name this new reptile Algoasaurus Bauri, after the 

 late George Baur, whose early death removed from the ranks of 

 investigators one who could ill be spared. 



VI. — Note on a Pillow-lava apparently forming a continuous 

 HORIZON from Mullion Island to Gorran Haven in Cornwall. 



By G. T. Prior, M.A., F.G.S. 



rpHE basalt of Mullion Island, with the intercalated radiolarian 

 X chert, is well known from the descriptions of Teall and Howard 

 Fox.^ It is a fine-grained minutely vesicular basalt, consisting 

 mainly of radiating felspar laths and interstitial pale purplish-brown 

 augite, and occurring in peculiar pillowy or bale-like masses. 

 Owing to this curious structure and its intercalation with the chert 

 the basalt is considered to be a submarine lava. 



A well-marked horizon of radiolarian chert similar to that of 

 Mullion Island has been traced by Mr. Howard Fox ^ from that 

 island across the Lizard peninsula to Porthallow, and thence to 

 the other side of Falmouth Bay to Pendower and Gorran Haven. 



Lately, in the company of Mr. Upfield Green, I have made 

 a collection of igneous and other rocks from the north of the Lizard, 

 south of Helford river, and from the neighbourhood of Gorran and 

 Caerhayes on the other side of Falmouth Bay. Many of the volcanic 

 rocks are almost precisely similar, both in pillow structure and in 

 microscopical characters, to the Mullion Island basalt. The following 

 is a list of the localities, besides Mullion Island, at which this 

 particular kind of basalt was found : — 



Tregidden. — The basalt occurs here in two quarries on opposite 

 sides of the stream ; in one of them to the east the pillow structure 

 of the rock is well marked. In microscopical characters the basalt 

 is precisely similar to that of Mullion Island. It is finely vesicular, 

 and shows minute interlacing felspar laths with much interstitial 

 pale purplish-brown augite, and little or no iron-oxides. It varies^ 

 in coarseness of grain, and in parts is much altered, so that the 

 augite is unrecognizable. To the west of Tregidden, nearer to 

 Mullion Island, precisely similar basalt was met with at Trethewy 



1 Quart. Journ. Geol. Soc, yoI. xlix (1893), p. 211. 



2 Trail,?. Eoy. Geol. Soc. Cornwall, xii (1), 1896, p. 39. 



DECADE V. — vol,. I. — NO. IX. 26 



