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Geology rf Wiltshire. 



layers of stone varying very much in their respective thicknesses, and separated 

 from each other by natural joints or " partings." In the oolite these partings 

 are extremely thin ; they appear as if marking certain periods in the formation 

 of the rock, during which the progress of the deposition was arrested, and the 

 stone allowed to harden before fresh accumulations of calcareous matter were 

 thrown down upon it. Out of the whole mass of freestone forming the core of 

 Box-hill, only those beds are quarried which are known to produce good stone. 

 The number, lie, and position of these were ascertained with considerable 

 accuracy during the progress of the tunnel, whose shafts, penetrating through 

 the whole formation, afforded the best possible opportunities for an examination 

 of its constituent members. The average depth of the workable beds varies 

 from eight feet to thirty feet, and their respective thicknesses range from six 

 feet to one foot. The uppermost of them is only about ten inches through, and 

 this is called the "picking bed," for a reason which will become clearer as we 

 proceed. The accompanying sketches will help to render our explanations more 



OF WORKINC. 



intelligible. Here figs. 1 and 2, represent the section and elevation of a working 

 recently opened ; its various beds of stone being shown at A, B, C, D, E, F. In 

 the uppermost of these (A), previously denominated the picking bed, an exca- 



