606 J. V. LUWlS OtllGIlSr OF PILLOW LAVAS 



found with alternating coarse and fine tufi beds above. VThen the waters 

 finally cleared, a teeming fauna again overspread the spot. 



Scotland. — South of Tayvallich, in Argyll, Peach*^ found sheets of 

 slaggy andesitic basalt, with marked pillow structure (plate 21, figures 

 1 and 2), intercalated with the black schist and limestone of the Dal- 

 radian series (pre-Cambrian). There are also accompanying beds of 

 tuffs and agglomerates. According to Dewey and Flett,^^ these rocks 

 continue through Argyll past Loch Awe and representatives are again met 

 with at Ar dwell, in Banffshire. Pillow structure in the Lower Carbon- 

 iferous lavas near Millstone Point, Argyll, northeast of the coast of Arran, 

 is clearly shown in a photograph that I have obtained from the Geo- 

 logical Survey of Great Britain. 



In Bute j)illow structure occurs in the basic lavas of the Cement Group 

 (Lower Carboniferous) at Corrie, in the Island of Arran; also in similar 

 lavas of supposed Arenig age at Torr na lair Brice, north side of Xorth 

 Glen Lannox, Arran, as shown by the Survey photographs. 



Pillow lavas in the Silurian rocks of the south of Scotland, particularly 

 well shown along the coast near Ballantrae, in Ayrshire (plate 20, figure 

 2), have been described by Peach, Home, and Teall.*^ The rocks include 

 a series of much altered basic and intermediate lavas and tuffs, the micro- 

 litic, nonporphyritic members of which show well developed pillow struc- 

 ture in many places. Am3^gdules are arranged in concentric layers and 

 are generally more abundant toward the outside of the masses. The pil- 

 loAvs range from a few inches to several feet in diameter and lie with 

 their longest axes parallel to the stratification of the sedimentaries. The 

 spaces between are filled in various places with calcareous matter, flinty 

 shale, chert, and jasper, the calcareous materials being confined mainly 

 to the surfaces of the flows. 



Geikie*^ has described the pillow lavas in the Carboniferous rocks of 

 Fife, which are basic basalts of the "picrite type,^' many of them thor- 

 oughly vesicular from top to bottom and full of dirty green amygdules. 

 These are much decomposed, but others are fresh compact blue or black 

 basalts and in some places columnar. Some of the flows are partly one 

 and partly the other, the fresh parts being generally surrounded by the 

 decayed amygdaloid. 



^ B. N. Peach : Mem. Geol. Survey of Great Britain. Scotland. Summary of Progress 

 for 1903, p. 69. 



*7Geol. Mag., vol. viii. 1911, p. 241. 



*s B. N. Peach. John Home, and J. J. H. Teall : The Silurian rocks of Britain. Mem. 

 Geol. Survey of Great Britain, vol. i, Scotland, 1899, pp. 84-86, 367, 431, and pis. 1, ii, 

 Iv, V, vi. 



^ A. Geikie : The geology of central and western Fife and Kinross. Mem. Geol. Survey 

 of Great Britain. Scotland, 1900, pp. 54, 55, 62, 64, 69, 72, 74. 



