150 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



angular, and concentric spheroidal concretions, are distributed 

 irregularly through the softer marly mass. They all have a 

 variegated or red-marl-like basis, and pass insensibly from the 

 most indurated and tough varieties into a friable red marl. The 

 more typical marly variety is often of a globular, concretionary 

 structure, and is composed of concentric layers, which are 

 variegated red, buff, and pale green in colour, and are so friable 

 that, under a slight blow of the hammer, they crumble into small 

 cuboidal or polygonal fragments. The intermediate varieties are 

 characterised by different degrees of induration. Most of them 

 are rather tough than hard, and towards the western extremity of 

 the trap have the aspect (but evidently not the mineral structure) 

 of some of the Lizard serpentines ; and throughout the exposed 

 range of this ledge for about a hundred yards, both the hardest 

 and most friable varieties are traversed by numerous veins of 

 red and white fibrous gypsum, or of fibrous gypsum and cal- 

 careous spar. 



The softer and more friable variety is best seen at the Dripping 

 Well (a broad chasm in the neighbourhood), where it has been 

 raised beyond the reach of the sea. It is there intersected by 

 numerous fine lines of fibrous gypsum and calcareous spar. A 

 little to the west the entire bed has been exposed to the action of 

 the waves ; but a prominent serrated ledge, in advance of the 

 cliffs, marks the continuation of the harder and more crystalline 

 variety further westward, for the distance of about a hundred 

 yards. 



No. 5., which rests conformably upon the last bed, is a pale red 

 quartz rock, exactly like the red quartz rock of the Hotwells and 

 Brandon Hill, near Bristol, which has been supposed to represent 

 the millstone grit of the northern counties. 



No. 6. is much the same as the last ; but is more calcareous. 

 No. 7. is the ordinary grey mountain limestone. Some of its 

 beds, on the shore, are parted by a red marly substance, similar to 

 that of the trap rock, No. 4. 



No. 8. is apparently a raised beach. It consists of sea sand, 

 aggregated together into a tough compact mass by calcareous in- 

 filtration, and rests on an accumulation of stones so imperfectly 

 rounded as to be neither a conglomerate nor a breccia. The sand 

 itself has the character rather of the sea sand of Cornwall than of 

 the sand of Uphill and of the other adjacent bays, containing, as it 

 does, a considerable proportion of highly comminuted shells. 



With regard to the trap rocks, there can be no doubt that they 

 were ancient lavas, erupted, at two distant periods, over the floor 

 of the sea, while the mountain limestone was in process of forma- 

 tion ; the interval of duration between them being indicated by 

 the interposed bed of limestone, No. 3., of which duration it is 

 the measure. But where did the trap come from, and how was it 

 generated ? If I could not appeal to the case of the Bleadon 

 cutting, as sufficient proof of its having originated in the fusion 

 and conversion of mountain limestone and other underlying de- 



