ALUBT SHALE. 



\m 



matter, which occurs in various parts of the alum rock, seems to 

 be akin to rock-milk. It contains, however, a mixture of alumine, 

 or pure clay, along with calcareous matter. 



Notwithstanding the compactness of this part of the rock, it has 

 its vertical seams, or cross veins, intersecting one another obliquely, 

 and dividing it into rhomboidal blocks ; though its veins are fewer, 

 and its sections are consequently lai'ger, than what we see in the 

 higher parts of the rock. As this schistus, like the chalk of Flam- 

 borough, has a tendency to split vertically; so, like that, it is liable 

 to be penetrated by the sea, which forms in it curious recesses and 

 grottos. This remark applies not only to this part of the beds, but 

 to the alum rock in general. One of the most noted caves in the 

 schistus is Hob-hole in Runswick bay, which some years ago had a 

 most romantic appearance, having a double pillar in the middle of the 

 enti-ance, as represented below. 



The pillar has been demolished by the waves ; but the cavern is 

 still 70 feet long, and' 20 feet wide at the mouth.* 



* For an account of llie siiptrstitioiis connected willi Mob-hole, presumed' to have biicii 

 the rnsideiice of a A:;6gobliii, see Hist, of Whitby and the Vicinity, H. p. SS3. 



2 M 



