Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/58

 46 by several layers of indurated clay or argillaceous stone. These intervening beds possess in conjunction a very uniform thickness of ten or eleven yards, and are irregularly penetrated by veins of the fossil salt. Though the evidence on the subject is not entirely of a positive nature, there seem strong grounds for believing that the beds of rock-salt at Northwich are perfectly distinct from any others in the salt district, forming what the Germans would call ligende stocke, lying bodies or masses of the mineral. It will readily be conceived that there is much difficulty in acquiring precise information with respect to the extent and limitation of these great masses, and that there are many sources of error to which such an inquiry is liable. There are, however, a few leading facts upon which dependence may be placed, and which will be admitted to furnish fair grounds for deduction.

It would appear that the great beds of rock-salt at Northwich assume a general longitudinal direction from north-east to south-west, the line which has been traced upon them in this direction being a mile and a half in length, and no direct evidence existing that they may not extend further in these points; while their transverse extent, as measured by a line at right angles to the former, is much more limited, probably not exceeding in any place one thousand three hundred or one thousand four hundred yards. Several circumstances concur in giving probability to this statement. Let two parallel lines, drawn from NE to SW, with an intervening distance equal to about half their length, be employed to designate the supposed extent of the subjacent rock-salt. In a mine which approaches very nearly to the eastern limit of the area thus formed, the upper bed of rock-salt was actually worked through in an horizontal direction on this side, and discovered to be going of with a very rapid declivity. A similar fact has been stated with respect to