MONIAN SYSTEM OP ROCKS. 



479 



Fig. 2. — View in Borth Saint, Roscolyn. 





1. Upper quartzite. 2. Quartz-vein bed. 3. Red Beds. 



4. Lower purplish beds. 5. Broken red slates &c. 



The nearly vertical lines are lines of cleavage. 



these seem to be very local : and though under the action of the 

 weather all the surface holes quartzitic, there is no quartzite proper 

 to be seen in either section or cliff. There is no other bed in the 

 Roscolyn series sufficiently characteristic for correlation, so we are 

 left in doubt whether all these northern beds are newer, or changed 

 in the new area from their old form. On the whole, I regard the 

 series as ascending from the South-Stack end, thus forming a great 

 synclinal, of which the trough is occupied by the sea and the two 

 ends are exposed. 



On this supposition we may see the succession of the lowest beds 

 in a deep gorge in the cliff at Gogarth. Here the beds lie in a great 

 fold, rising on the whole to the S.E., though there is very clear 

 cleavage to the N.W. The beds are alternately soft and hard, the 

 softer being a massive felspathic rock, more like volcanic dust than 

 any yet seen, and several of the harder ones showing the festoon- 

 ings of the lower side from pressure. The changing character of 

 the rocks can best be seen by looking at the cliff from the light- 

 house island, where more than 80 beds, of thicknesses varying 

 from 8 inches to 3 feet, can be counted. The undulations are here 

 so strong that the actual dip may be doubted; but its average can 

 be obtained by following a single bed in its passage along the cliff 

 (see fig. 3). So far the average dip is to the S.E.. The magnificent 

 bird-gorge, where the gulls, the kittiwakes, the razorbills, and the 

 cormorants assemble in thousands, is occupied by a synclinal, and 

 beyond this the shore is inaccessible ; but in the deep gorges of the 

 cliff the crests of the anticlinals of contortions point S.E., which 

 indicates an average dip to the same point of the compass. In the 

 nameless bay which now succeeds, the rocks are still beautifully 



Q.J.G.S. No. 175. 2 k 



