96 Geology of Wiltshire. 
the different beds composing the surface rocks are an accurate copy 
of the details given in the Ordnance sheets, very recently issued 
from the Geological Survey, as the much smaller scale of the map 
would admit of, and are consequently more to be relied on than 
those given in Smith’s original map. I subjoin a Table of the 
Ascenpinc Srrres oF Rocks (In WitsHiRre), 
According to latest divisions of Geological Survey. 
Sir C, LYELL’s CLASSIFICATION, 
1. Lias shale, clay, or Marlstone 1 Lias. 
2. Sand of inferior oolite 
3. Limestone of do. \2 Inferior Oolite. 
Lower : 
avs 4, Fuller’s earth 
Oolitic BulGreatonlié 
group. inane Sapo 3 Great or Bath 
6. Forest marble Oalife: 
7. Cornbrash 
Middle 8. Oxford clay 
4 Oxf } 
Oolitic 9. Calcareous grit Z Pte a 
group. | 10. Coral rag 5 Coral rag. 
c 11. Kimmeridge clay 6 Kimmeridge clay 
Pper | 19. Portland sand ; 
iti ; . 7 Portland beds. 
Dolitie 138. Portland stone crane as 
SrOUP: 114, Purbeck 8) oe Por beds 
ite 
Cretaceous } 16. 
group. ie 
. Chalk 
Lower Green sand 
Gault 
Upper Green sand 
9 Lower green sand 
10 Gault 
11 Upper green sand 
12 Lower White 
{ without tins | Chalk 
13 Upper White 
Lower Ps Plastic clay 14 Lower Eocene 
Eocene. (20. London clay 15 
Middle )21. Lower Bagshot sand Hg 
Eocene. es Bracklesham sand inte 
Alluvium. Mammalian Drift 17 Post Pliocene 
On reference to the map it will be seen that nearly a full half of 
the surface of the county consists of chalk, with or without a thin 
coating of Tertiary, or yet more recent sand, clay, and gravel. 
This mass of chalk forms our Down-country, being the western por- 
