217 
LOWER CHALK—LINCOLNSHIRE. 
The Inoceramus Beds are generally from 4 to 0 feet thick, and 
lie in two or three courses, with marly partings. They consist of 
rough grey gritty chalk, often somewhat nodular, and always full 
of Inoceramus shells. 
The remainder of the zone consists of rather rough greyish chalk 
in thin irregular beds, with partings of shaly mail in the upper 
part. Am. (Schloenbachia) varians is not very common, while 
Holaster subglohosus and Discoiclea eylindrica occur in most 
exposures. 
Beleraniie marl. 
/ 
Zone of Offaster / 
sphcericus. ' 
\ 
/ 
Zone of 
Ammonites 
varians. 
K 
Selbornian. 
Grey and purple marl. 
Pinkish-yellow chalk. 
Greyish-white chalk 
Pink chalk. 
The grey bed (Totternhoe Stone). 
Grey chalk. 
Inoceramus Beds. 
Sponge bed, yellow and pink. 
Red chalk. 
Red sandy marl. 
Fig. 31 .—Vertical Section of Lower Chalk in Lincolnshire. 
The Zone of Offaster sphaericus.— In consequence of the 
extended range of Holastar subglobosus in Lincolnshire and York¬ 
shire, Offaster sphcericus has been adopted as the index of the 
higher zone. At its base there is a small representative of the 
Totternhoe Stone in the form of one or two beds of hard rough 
grey chalk. Sometimes it occurs as a massive bed of hard nodular 
chalk breaking into large blocks, but more often there are two 
beds, the lower one rough and nodular, the upper one compact, 
massive, and blocky. This gret chalk is generally from 3 to 4 feet 
