154 PROFS. LLOYD MORGAN AND REYNOLDS ON THE [May I904, 



Some of the rocks are highly-amygdaloidal (Woodspring, Spring 

 Cove, Goblin Combe — western exposure, Milton Hill, and Uphill in 

 part). Others are not (Uphill in part, near Cadbury Camp, Milton 

 Hill in part, Goblin Combe — eastern exposure). 



(B) The Tuffs. (PL XVII, figs. 4-6.) 



(1) Description of the Tuffs from Middle Hope, 



Woodspring. 



The prevalent type of tuff in all four exposures is a rather soft, 

 dull-green, much-decomposed, and earthy-looking rock, with patches 

 and veins of calcite and many small green lapilli, which in the 

 sections examined do not, as a rule, reach a greater length than 

 2 millimetres. 



In section the lapilli are seen to consist entirely of a highly- 

 amygdaloidal rock, with a groundmass which is almost completely 

 isotropic, and must have originally formed a basic glass, now altered 

 into green palagonitic material. The amygdules are generally 

 composed of a chloritic mineral, sometimes of calcite. The matrix 

 in which the lapilli are embedded usually consists of well-cleaved 

 calcite, through which a%e scattered numerous minute ashy frag- 

 ments similar to the larger lapilli. In addition to these there occur 

 at certain levels, especially in the ashy limestone above the trap 

 at the westernmost exposure, large lapilli, frequently reaching a 

 length of an inch or more, of a quite different type from those 

 described above. The groundmass of these lapilli, which is much 

 irou-stained, contains numerous felspar-needles, but apart from 

 them is isotropic, and shows no sign of palagonitic modification. 

 The vesicles are very abundant, and in one slide are filled with 

 well-cleaved calcite, precisely similar to that forming the main 

 mass of the surrounding limestone in which they are embedded. 

 In a second slice the only difference is that the calcite filling the 

 vesicles is, as a rule, granular and not well cleaved. 



(2) Description of the Tuffs from Goblin Combe. 



Most of the rocks are, in the main, limestones of a non-oolitic 

 character, but they contain a variable proportion of oolitic grains 

 and many quartz-grains, with ashy fragments as well. The pro- 

 portion of ashy fragments is far greater in some of the rocks from 

 the eastern exposure than in any of those from the western, but 

 nearly all are best described as ashy and gritty oolitic lime- 

 stones. Sections taken from the lowest bed in the more westerly 

 exposure show that angular quartz-grains are far more plentiful 

 than either lapilli or oolitic grains. The latter reach a diameter of 

 4 millimetres. Some of the lapilli are identical with the basalt, 

 which, as already mentioned, probably underlies the ashy limestones; 

 they contain the same patches of yellow chlorite or serpentine, and 



