140 DESCRIPTION OF THE STRATA 



of shale, somewhat sandy and micaceous, with ironstone seams and 

 nodules imbedded in it, principally occupying the higher part of the 

 bed, but often descending more or less towards the lower part. 



Below this portion of the aluminous strata, we find interstratifi- 

 ed with the shale, some beds of aegillo-calcareous sandstone 

 WITH SHELL LIMESTONE. This member of the series (No. 11) forms a 

 very conspicuous band in the aluminous cliffs, wherever it rises above 

 the sea. It consists chiefly of sandstone, arranged in various beds ; 

 two or three of which are generally thick and massive, while the rest 

 are more thin and schistose. The sandstone is of various colours ; 

 such as, ash grey, blueish grey, pale brown, and yellowish grey. It 

 abounds with specks of mica, particularly in the schistose beds or 

 seams ; which also contain the greatest number of shells. 



In the upper part of these beds there are two or three seams of 

 shell limestone, consisting almost entirely of shells, with very little 

 cement. These seams are seldom more than a few inches in thick- 

 ness. Sometimes a seam of this kind may be found adhering, like 

 a crust, to a bed of sandstone. It is also not uncommon, in this 

 member of the strata, especially in the upper part of it, to find sand- 

 stone beds or seams covered with a crust of ironstone. 



All these rocks, of whatever kind, are interstratified with seams 

 or thin beds of shale ; which, however, is often so sandy and 

 micaceous, as to differ very little from the schistose sandstone. The 

 whole together occupy a space of about 60 feet, at Boulby ; but in 

 several places they are not so thick, while in other places, particu- 

 larly at Huntcliff, and between Skinningrave and Lofthouse alum- 

 house, they swell to the thickness of 80 or 100 feet, a large portion of 

 the cliff consisting of sandstone beds, parted by thin seams of shale. 



As the strata now described (marked n in the Section) rise up at 

 Staiths, we may name them the Staiths beds. 



We are now arrived at the lowest alum shale (marked o), 



