136 DESCRIPTION OF THE STRATA. 



extremely minute shining crystals, which however are scarcely 

 discernible with the naked eye. This kind of limestone is found in 

 other parts of Britain along with the blue lias, and is called the hlaeh 

 or fetid lias* 



That part of the alum rock which abounds with these large mas- 

 ses, or imperfect seams, of limestone, may be estimated at ten feet ; 

 though it is sometimes less, and sometimes considerably more. This 

 part of the rock we may distinguish by the name of the Sandsend beds, 

 as in tracing the series from Whitby to the heights at Boulby, we find 

 these seams of lias first making their appearance on the shore below 

 the Sandsend alum works. 



We now descend to the next member of the aluminous strata, 

 which consists of hard and compact alum shale. No. 8 in the 

 Boulby series. This also is not a new bed, but a continuation of the 

 great bed of schistus. It differs from the upper part of the bed, 

 chiefly in being much more solid and compact, and in containing less 

 sulphur: and it differs from that part of the rock last described, in 

 containing fewer imbedded nodules or masses, and those generally 

 smaller. In other respects, its nodules are similar to those in the 

 schistus above it. They consist of limestone and pyrites, and are 

 extremely hard ; and owing to the hardness of the rock itself, they are 

 not very easily detached from their beds, so that they often stand out 

 from the face of the rock as protuberances. This part of the rock 

 often appears as a firm perpendicular wall, more or less incrusted 

 with the rusty coating formerly mentioned. Sometimes it is also 

 stained with a white substance, washed down by the rains, or oozing 

 through the cross seams of the higher parts of the strata. This white 



* See Mr. Horner's Essay on the Geology of Somersetshire, Geological Trans. III. p. 368. 

 There are several varieties of fetid limestone. A fibrous and radiated kind, of a brown colour, 

 occurs in the Sunderland rocks. A fetid limestone, of a greyish white colour, is found at the 

 Dead Sea, and at some of the Egyptian pyramids. See Clark's Travels, II. p. 538. III. p. 130. 

 Some of these varieties are called stink-stone. The emission of a gaseous sulphuretted hydro- 

 gen is considered as the cause of the strong odour. 



