LOWER CHALK—NORTH DORSET, 
103 
CHAPTER IX. 
THE LOWER CHALK IN NORTH AND WEST DORSET, * 
SOMERSET, AND PARTS OF DEVON. 
In this chapter it will be convenient to describe not only the 
exposures along the main outcrop of the Lower Chalk through 
Dorset, but also those in the outliers near Crewkerne, Chard, and 
Axminster, in the area vhiere the counties of Dorset, Somerset, and 
Devon meet. 
We shall regard North Dorset as extending from Melbury 
Hill, near Shaftesbury, to Melcombe Bingham, which lies about 
half-way between Blandford and Cerne Abbas. Along this tract 
the general strike of the Chalk is from north-east to south-west, 
while near Melcombe Bingham it changes to an east and west direc¬ 
tion. The remaining part of the county will be described under 
the head of West Dorset; and thirdly, the still more western 
outliers will be noticed. 
1. North Dorset. 
In the northern part of the county the Lower Chalk has much 
the same facies as that of Hampshire and the Isle of Wight, but its 
thickness rapidly diminishes toward the south-west. From about 
180 feet near Shaftesbury it diminishes to about 100 feet at Mel- 
combe Bingham. This diminution appears to result chiefly from 
the thinning of its lower portion, the Chalk Marl or zone of 
Ammonites varians. This zone can be traced with a normal 
facies and with the usual fossils as far as the valley of the Stour, 
but west of that changes take place, and the marly beds either 
thin out or change laterally into purer chalk. Thus, by Ibberton, 
Woolland, and the Melcombes the vdiole division consists of soft 
chalk, without any hard beds, and the only marl is that which 
forms the summit of the stage. In this part of the area the 
lowest beds are soft and mealy, the higher beds are firmer and more 
blocky, but fossils are rare throughout, and it is really impossible to 
separate the zones of Ammonites varians and Hoi aster subglobosvs 
from one another. I surveyed part of this tract in 1891, and 
Mr. Hill continued the examination of the more westerly part 
in 1893. 
Zone of Ammonites varians. 
An excellent section of the passage beds between the Greensand 
and the Chalk is exposed in a large quarry on the north side of 
Melbury Hill, tw T o miles south of Shaftesbury. The passage hgre is 
