392 MARLOES BAY. — COAST SECTION OF UPPER SILURIAN ROCKS. 



Mario es Bay. (See Map.) 



The western shores of Broad Sound, of which Marloes Bay is a part, present a full 

 succession of all the rocks of the Silurian System, from their junction with the Old Red 

 Sandstone at Hook Point, to their passage into strata of the Cambrian System in the 

 extreme headlands of Wooltack Park and the Isle of Skomer. This transverse section 

 exposes the strata rising from beneath each other for not less than two miles, dipping 

 to the S.S.E. at an average angle of at least 45°. The thickness of the Silurian System 

 in this one spot is, therefore, very considerable, though it occupies so small a breadth 

 upon the map. 



The above wood-cut represents the upper portion of this series, surmounted by the Old Red 

 Sandstone. The lower strata, associated with trap, appear in the vignette, p, 389. 



Descending Section (Marloes Bay). (PI. 35. f. 10.) 



Red and green rab or base of the Old Red Sandstone, alternating with grey sandstone, as seen at the end of the above 

 wood-cut and coloured section. (PI. 35. f. 10.) 



1 . Dull greenish grey sandstone and schist, in parts argillaceous, very minutely micaceous, and not unlike the Upper 

 Ludlow Rock, except in being harder and thicker bedded, dip 35° S.S.E. It passes upwards into the red rab. 



2. A succession of thin-bedded sandstones and shaly beds of various colours, some weathering to deep ochreous yellow, 

 others to white. They contain casts of fossils, including Crinoidea, &c. As these beds are on the whole much softer than 

 No. 1, they have been worn into a cove by the sea. They are in parts pyritous. 



3. Hard, finely laminated, grey, slightly calcareous sandstone of considerable thickness, traversed by white veins of cry- 

 stallized carbonate of lime, with imperfect casts of trilobites and other fossils. In part a slight conglomerate appears, with 

 sandy courses, the edges of which are marked by protoxide of iron, which occurring in blotches somewhat resembles carbo- 

 naceous markings. Corals very abundant. 



4. Hard thick-bedded grey sandstone with white quartz veins. 



5. Calcareous sandstone and shale, with veins of white carbonate of lime, with many corals, particularly in the upper 

 parts. The beds dip about 65°, whilst the planes of slaty cleavage dip 85°. N.B. The cleavage planes are visible in the 

 schistose beds only, being imperceptible in the intervening strata of thick-bedded sandstone. (See wood-cut, note, p. 360.) 



6. Beds 3 to 4 feet thick, more or less calcareous, with corals, imperfect casts of shells, tentaculites, and trilobites, pro- 

 bably heads of Calymene Blumenbachii. 



7. " Bands of ferruginous thin-bedded sandstone, with beds of intervening shale; where the latter is worn out, the highly 

 inclined sandstones form the top of the cliff, and are called the " Three Chimnies." A slaty cleavage, oblique to the lines 

 of stratification, is impressed upon the mass, and a few quartz pebbles mark the laminse of deposit as they approach towards 



