646 



ME. C. A. MATLEY ON THE 



[Aug. 1899, 



to be mistaken for a bedding-plane, but the bands in the two series 

 strike against each other. Its true character can be seen more 

 plainly in a little creek that has been eroded at right angles to the 

 trend of this cliff near its seaward termination, where the thrust 

 AB can be seen rising steadily to the westward at an angle of 20°, 

 and bringing the green beds over the younger Ordovician. This 

 little creek has been eroded along another overthrust CD, which has 

 here a nearly east-and-west course, and again brings up the Green 

 Series. The thrust CD is a somewhat later movement than AB, 

 and its pressure has bent the earlier thrust-plane, thus accounting 

 for its synclinal curve. The green beds are highly crushed and so 

 broken as to be practically crush-breccias, and are much rolled out 

 near the junction. The Ordovician rocks are also much crushed 

 (N.A. 89 & 90). 



The later thrust has here an inclination of 60° to the horizontaL 

 Its course can be readily followed in a west-north-westerly direc- 

 tion, first across the shore and then inland in front of the lower 



'^o/y,; C arm el 



Fig. 2.— Sketch-map of 



ttie North-western corner ^ha.6ed areas = Ordovician.. 



of ANGLESKY t/ns/jac/ed.areas^pre-Llandei'IOa 



Scale .! 2 inches to 1 fHfUe..' 



beacon. Its inclination decreases to 30°, and continues to flatten^ 

 as shown by the course of its outcrop on the rising ground. It 

 finally passes out to sea in the unnamed Perth south ot Forth y 

 "Wig, where an almost level platform has been worn along the 

 junction. The underlying beds are the Ordovician slates. The 

 overthrust beds are greenish-grey gritty phyllites, as a rule highly 

 contorted and smashed, and showing microscopically evidences of 

 movement. They are succeeded at Carmel Head by beds with 

 broken limestone and quartzite, where they form almost a ' crush- 

 conglomerate.' In Forth Gron, hading north-west at 45°, can be 

 seen another thrust forcing the Green Series over contorted grey 

 Ordovician slates ; but perhaps enough detail has been given to 

 prove that the asserted interstratifications of the two series are the 

 deceptive results of earth-movements. Fig. 2 shows the course of 

 the principal faults and thrusts in this corner of the island. 



