Vol. 60.] 



IGXEOUS ROCKS AT SPRING COVE. 



163 



^Near the middle of the sheet, covered and underlain by massive 

 lava, is a band 5 to 6 feet wide, with a dip roughly parallel to the 

 other lenticular masses, consisting of a confused mass of coarse 

 tuffy material, made up of angular fragments of lava 1 to 2 inches 

 across, embedded in a fine red-and-green matrix, and containing 

 lenticular cakes of vesicular lava, phacoids (often broken and 

 torn) of limestone, and higher up the cliff larger spheroidal lumps 

 of lava. The whole band suggests forcibly the augen-structure 

 characteristic of gneisses. It probably represents, however, a torrent 

 of agglomeratic material that flowed down a slope on the surface 

 of an already-extruded bed of lava, carrying in among the finer 



Fig, 4._, 



coarse ar/r/lom e ra te 

 f-lavcf. 



Lim. = Limestone 

 Bas. = Basalt. 



lapilli larger, irregular, and plastic masses of scoriaceous basalt-lava 

 of the nature of bombs, together with lumps and fragments of lime- 

 stone, which from their form and broken character suggest that 

 they were ejected from the vent with the basaltic material (fig. 4). 



In all cases where the phacoidal or lenticular structure is seen, 

 whether on a large or on a small scale, the material forming the 

 groundmass is fragmental and tuff-like, while the included phacoidal 

 masses consist of vesicular lava, or limestone, or very occasionally 

 masses of coarse tuff (figs. 2, 3 & 4). 



A thin slice of the typical tuffy matrix [20] shows small sub- 

 angular or rounded, closely-fitting, equal-sized lapilli, about an 



31 ? 



