MIDDLE CHALK—-LINCOLNSHIRE. 
479 
The “ columnar bed ” is almost always clearly discernible, though 
in some places the vertical joints are less numerous than in 
others. 
The overlying chalk is of a pure creamy-white compact, evenly 
bedded, and containing nodules of grey flint, which are generally 
arranged in layers, though in some of the higher beds there are 
scattered flints of irregular elongate shape between the regular 
courses of flints. These grey flints adhere closely to the chalk in 
which they are embedded, and are traversed by the same joint 
planes as the surrounding chalk, so that as the rock is quarried and 
breaks away along these joint planes the fracture passes evenly 
through both chalk and flint, each portion of the flint nodule re¬ 
maining in the block of chalk to which it belongs. In consequence 
of this peculiarity every layer of flint exposed in a quarry is visible 
at a glance. Thin continuous layers, or floors, of flint occur 
occasionally, but are not numerous. Thin seams of dark grey 
marl, or marly clay, are of frequent occurrence. Fossils are 
extremely scarce, with the exception of Inocerami belonging to 
species which are generally referred to 7. Brongniarti and 
7. Cuvieri. The characteristic Terebratulina has not yet been 
found in this county. 
With respect to the thickness of this chalk with nodular flints, 
which evidently represents the Terebratulina zone, we can only 
say that it is probably from 70 to 80 feet. It is only recently 
that Mr. Hill has found evidence of the zone of Holaster 'planus near 
Louth, and has consequently proved that there is Upper as well as 
Middle Chalk to the north of that town.* This discovery excludes 
from the Middle Chalk most of the higher beds which contain 
thick continuous floors of flint, and restricts it to the chalk with 
nodular flints as above described. 
The small thickness of the zone of Rh. Cuvieri, and the appearances 
at the top of it, suggest that the plane of division between it and the 
overlying zone represents the lapse of a certain period of time,during 
which no deposition took place, even if there was not some removal 
of material by current action. 
Stratigraphical Details. 
Zone of Rhynchonella Cuvieri, 
The chalk of this zone is exposed in many of the chalk pits which 
have been opened along the range of the Lincolnshire Wolds. 
Details of these will be found in the memoirs descriptive of Sheets 
84 and 86 of the Geological Survey map, but a few of the best 
sections are given below. 
Near the southern end of the Wolds there is a good section 
through these beds in the quarry north-west of Claxby. A fault 
* See “ Note on the Upper Chalk of Linconshire,” by W. Hill, in Geo], 
Mag., Dec. 4, Yol. ix., p. 404 (1902), 
