326 Some Observations 



the valley on eadi side, are formed of a vellowish grey sandstone 

 of a coarse texture, and containing many scales ot grev mica. 



The great body of the salt forms a rugged precipice, which is 

 reckoned between 400 and 500 feet in height at the upper ex- 

 tremity of tile A-alley, and is covered by a thick bed of the clay 

 above mentioned. 



The precipitous form is partly owing to the manner in which 

 the mine has been wrought for a series of ages. There is no ex- 

 cavation ; but the salt has been procm-ed by working down per- 

 pendicularly as in an open quarry. The lowest part of t!ie pre- 

 sent works has a solid floor of jjure salt which is not al)ove the 

 level of the bottom of the vallev where no salt is found ; but the 

 real depth of the bed of salt has never yet been ascertained. The 

 upper surface of the salt is not level ; but appears irregularly ele- 

 vated, according to the general outline of the hill in which it 

 occurs. 



The salt has been usually represented as forming an entire 

 mountain : but though it here appears supplying the place of 

 common rock, vet from its being confined to this vallev, and not 

 attaining so high a level as the surrounding hills, it wovdd seem 

 more correct to consider it as a mass or bed of salt filling up a 

 valley, than as constituting a mountain, which according to 

 some authors* is a league in circimifeience. Tiiese dimensions 

 could only be obtained by considering the neighbouring heights 

 as formed of this mineral; a supposition not countenanced by 

 my personal observation, nor by the best information which I 

 could collect on the spot. 



The surfaces of the salt precipice which have been long ex- 

 posed to the weather are not smooth, but cut into innumerable 

 shallow channel-;, running in a tortuous manner, and divided 

 from each otlier by thin edges, often so sharp as to cut the hands 

 like broken glass. The channeled surface is evidently. produced 

 by the action of the v.'inter rains, which have given the whole a 

 striking resemblance to the surface of a mass of ice, which had 

 been partially thawed and again frozen. 



The general colour of the exposed surface is grevish white, with 

 here and there a tinge of pale reddish browu, from tin." colouring 

 matter of the superincumbent bed of dav. Towards the ex- 

 tremities of the mass of salt, extremely thin lavers of a pure and 

 plastic clay are insinuated between layers of salt, so as to give 

 it the waved delineations wliich often occur in some species of 

 calcsinter. The general mass of salt is however of the greatest 



* Intrnduccion a la Hisloria 'Nutund y a la Gcogruftn Thku de Espana, 

 por Don Guillermo Bowles. — Madrid, 1775, — Dillon, wiio traoslates him, 

 Laborde, Ilineraire dcscriptij] &c. 



purity J 



