306 Sectional Officers’ Reports. 
LIMESTONE CONCRETIONS AT SALTERSFORD. 
During the years 1908-9 the Grantham Waterworks 
Company constructed a large Reservoir in the Witham Valley at 
Little Ponton. The excavations went through a bed of 
alluvium about 14 feet thick, at the bottom of which was the old 
river valley in the upper Lias Clay. 
This bed of Lias Clay forms the bottom of the Reservoir. 
After the alluvium had been removed, heavy rains scoured 
the surface of the clay and it was noticed that the floor of the 
Reservoir was covered in a certain part with a course “gravel.” 
This “gravel” turned out to be limestone concretions, some of 
the individual specimens measuring 2 inches or more in diameter. 
When cut in section, many of them showed a concentric 
structure of limestone and clay surrounding a hardened nucleus 
of clay. 
In seeking to explain the origin of these concretions it is 
necessary to explain that the excavation through the alluvium 
reached to a depth of 10 feet below the present bed of the river 
and showed that formerly a small lake had existed here, and 
that the present river bed is excavated in the alluvium which 
filled up this lake. 
Also, on the opposite, or West side of the river, there is a 
spring, (now taken into the mains of the Waterworks Co.), which 
is thrown out by limestone resting on Lias Clay. The spring 
water contains Carbonate of Lime in solution. Formerly, when 
the spring ran directly into the lake, some of its dissolved lime- 
stone would be released on the escape of carbonic acid gas, and 
this being deposited in the gently moving water of the lake would 
accumulate around any small moving body as a nucleus, and 
form a limestone ball. 
The alternating bands of limestone and clay seem to 
indicate that some sort of crystallizing force has been acting 
since the balls were formed, thus causing the limestone and clay 
to assume separate and distinct layers surrounding the nucleus. 
