Vol. 60.] IGNEOUS ROCKS OF THE BRISTOL DISTRICT. 141 



'hroughout the lower 7 or 8 feet of which big lapilli, reaching 

 a length of 2 inches, are fairly plentiful. (See figs. 2 & 3, 

 pp. 142-43.) 



(b) In the second exposure, three-quarters of a mile farther east, 

 alternations of reddish-brown or green tuff, with lenticular bands 

 of limestone, occur. But there is here no basalt, and the volcanic 

 series is thinner. 1 (See fig. 4, p. 144.) 



(c) The third exposure, some 200 yards still farther east, shows 

 brown tuffs and nodular or lenticular limestones in alternating layers. 

 The volcanic series is still thinner. 



(d) In the fourth, and easternmost, occurrence of the tuffs, 

 hitherto unrecorded, and lying two-thirds of a mile north-east of that 

 last named, they are reduced to 6 or 7 feet in thickness. But in 

 the lower part of the section there is no rock-exposure. Here, 

 however, a coarse fragmental deposit, 2 feet thick, with well- 

 marked lapilli, is one of the most characteristically-volcanic beds 

 of the whole series. The gradual attenuation of the volcanic 

 ejectamenta to the eastward and the occurrence of lava only in 

 the westernmost exposure, support the conclusion arrived at in the 

 ' Summary of Progress ' that the centre of volcanic activity pro- 

 bably lay yet farther west. 



1 The details of this section are as follows: — 



Thickness infect inches. 



20. Thick crinoidal limestone to the top of the cliff. 

 19. Weathered grit, with red shale visible at the 



eastern corner 10 



18. Limestone 12 



17. Green and red ash 5to7 



16. Sandstone, with vertical cylindrical bodies 2 6 



1 5. Fine ash 2 



14. Lenticular limestone-band 3to6 



13. Coarse ash, with highly-calcareous bands in the 

 lower 'part, numerous lai'ge fragments of lime- 

 stone and some of grit in the upper part 11 6 



12. Coarse ash 3 (i 



11. Brown ash, very much decomposed and veined... 1 2 



10. Limestone 4 



9. Ash as above (11), the upper part containing 



numerous lamellibranchs (Edmondia) 22 



8. Beddish crinoidal limestone 1 I) 



7. Ash, as above 2 



6. Argillaceous limestone 1 



5. Ash, as above 3 6 



4. Compact, somewhat argillaceous limestone 



3. Ash, as above 11 



2. Limestone, in bands 3 to 6 inches thick, with part- 

 ings of red shale and, at about a foot from 

 the top, one of green ashy material ; the upper- 

 most band of limestone is very argillaceous... 7 O 

 1. Massive limestone, with much chert, to the base 



of the section about 90 6 



