Vol. 52.] 



RASTERS CORNER OF ANGLESEY. 



619 



At the base is a peculiar grit, a few inches thick, composed 

 of quartz and detrital muscovite. Under the microscope certain 

 round bodies are seen in it, of which Dr. Hinde writes : — ■ The 

 rounded bodies in the slide are undoubtedly sections of sponge- 

 spicules, which are cut through some at right angles, others obliquely, 

 and very rarely in the direction of their length. The dark spot in 

 the centres of most of them is the axial canal of the spicule, now 

 filled with some dark mineral. In some cases the spicules have 



e.x.e. 



Fig. 1. — Section at Careg Onen, Anglesey. 



W.8.W. 



[Horizontal and vertical scale : 1 inch = 440 feet.] 



a = Schists. c — Ordovician Shales. 



h = Careg Onen Slates. d = Carboniferous Limestone. 



[The bedding oO should conform to their base-line throughout.] 

 Fig. 2. — Enlargement of X in fig. 1. 



x.x.w 



greeiiiili-grey slates green sc/iist ', 



in fig. 1. 



lying 



been squeezed out of shape. They are from *07 to '26 mm. in 

 thickness. I cannot say to what group of siliceous sponges they 

 may have belonged, for only these sections are to be seen. They 

 are now of microcrystalline (?) silica of the same character as is 

 usual with sponge-remains in Palaeozoic rocks. They seem to be 

 fairly numerous in the rock.' (See fig. 5, p. 020.) 



The slate and argillite also contain micas, which often lie at 

 right angles to the cleavage, and are bent. The nodules show no 

 certain organic structures. 



Q. J. G. S. No. 208. 2 u 



