10 A POPULAR SKETCH OF THE GEOLOGY 



a distance of five miles. It causes a down cast to the east of four 

 hundred and twenty feet.* A singular circumstance with regard to 

 this coal field is the fact that for the first three hundred feet from 

 the surface the water is perfectly fresh and soft, but below that depth 

 it is quite salt. Advantage has been taken of this circumstance, to 

 establish baths, but tbe salt is not in sufficient quantity for the profit- 

 able establishment of salt-works. 



The Swanington basin has a triangular shape, the apex being 

 about Lount, and the sides spreading out to Whitwick and Heather. 

 It dips gently to the south east, its edges being turned up to the south 

 west and north east respectively. It thus forms a long trough, the 

 northern end of which is raised, and which slopes gradually to the 

 south east till it becomes covered over with level unconformable beds 

 of new red sandstone. This covering of red marls and sandstones 

 is, at Whitwick and Snibston, about a hundred and fifty feet, while 

 farther south, at Bagworth, it is three hundred feet in thickness. 

 This basin is affected by very few faults, but the different beds seem 

 rather irregular in thickness and extent, the beds of coal being the 

 most constant. It is indeed, most probably, the same bed of coal 

 which is worked as the " main coal" over the whole of the Ashby 

 coal field, except at Lount and some other extreme points, where beds 

 lower than the " main" are worked. At Whitwick and Snibston a 

 mass of basalt, in one place sixty feet thick, is found in the upper 

 portion of the coal measures. This, where it touches the coal, has 

 burnt it into coke, and has changed a sandstone into a compact rock, 

 almost as hard as itself. Some trials have been made for coal south 

 of Bagworth, but nothing certain seems yet to have been ascertained 

 respecting the southern boundary of this basin ; and any workings in 

 that part of it must always be attended with considerable risk and 

 great expense, on account of the overlying measures of red marl. 



Mountain Limestone. 



Of the mountain limestone, which is the next formation in the de- 

 scending order below the coal measures, some small patches occur a 

 few miles north and east of Ashby-de-la-Zouch. Of these the larg- 

 est is that on which the villages of Staunton Harold, Calke, and 



• That is to say, that the beds east of this fault are four hundred and 

 twenty feet lower than the beds on the west of it, with which they were once 

 continuous. 



