628 MR. H. H. ARNOLD-BEMROSE ON THE MICROSCOPICAL [Nov. 1 894, 



Tideswell Lane head across the top of Cressbrook Dale into the 

 valley, and up the other side near Peter's Rock. It may be traced 

 from near the lane head to the highest house in Litton, the ' Peep 

 o' Day,' where it crosses the road. It is a bedded rock, and the 

 layers vary very much in coarseness. Subangular blocks, some being 

 12 to 18 inches in length, are found in it, especially in the upper 

 layers. There are also small pieces of a dark-coloured limestone. 

 There are good exposures on the roadside, and in two gullies in the 

 village. Climbing down into Cressbrook Dale, near Peter's Pock, 

 we find an outcrop of what is probably the same bed. It consists 

 of slabs 6 or 8 inches thick, which can be split into laminae of 

 about I inch in thickness, and which at first sight appear like a 

 fine-grained sandstone. This is no doubt what Farey 1 described east 

 of Litton as toadstone "so perfectly stratified that laminae almost thin 

 enough for house slates might be got in it." These slabs are accom- 

 panied by coarser laminae like those at ' Peep o' Day.' The bed 

 may be traced up the hill in the opposite direction to the dip. 



Proceeding down the valley, we pass about 15 to 20 feet of 

 limestone and then come to a bed of dolerite between 10 and 20 

 feet thick. It is vesicular, and decomposed at the base, amygdaloidal 

 and hard at the top, and compact towards the centre. It weathers 

 hard and rough, the harder portions standing out in lumps of the 

 size of a man's fist, and it breaks off into nodular pieces. In it are 

 a vein and several nodules of quartz. The Geological Survey maps 

 only one bed, but there are two, the lower one an olivine-dolerite, 

 succeeded by 15 or 20 feet of limestone with fossils ; and this in 

 turn is overlain by a tuff, whose laminae, varying in coarseness, denote 

 variations in the character of the outburst. 



A specimen of coarse tuff (sp. gr. 2-49) from this locality consists 

 •of lapilli in a cement of calcite. A lapillus contains olivine and 

 augite-crystals, and one felspar, all altered to calcite, in a black 

 base, containing vesicles filled with the same mineral. Others con- 

 tain a few skeleton-crystals, probably felspar in a brown isotropic 

 base, and others pseudomorphs of olivine in a dirty-brown base 

 having slight action on polarized light. The vesicles are filled with 

 calcite, or with a yellow, feebly double-refracting substance. 



In a specimen from the exposure on the roadside at ' Peep o' 

 Day' the lapilli are brown or grey, with green amygdaloids. 

 Under the microscope only one lapillus contains any crystals, and 

 these are pseudomorphs of olivine, felspars in very small lath-shaped 

 sections, and magnetite. Some lapilli are a mass of vesicles filled 

 with a material having radio-fibrous structure, and separated by thin 

 walls of a generally isotropic base. These lapilli were originally 

 more cellular than those from any other locality. 



A much more altered specimen (sp. gr. 2*42) consists of black 

 lapilli. A felspar-like mosaic, the pieces of which are too small 

 to test by convergent light, fills the vesicles and the spaces between 

 the lapilli. A specimen of the laminated tuff near Peter's Pock is 



1 ' General View of the Agriculture and Minerals of Derbyshire,' vol. i. (1811) 

 p. 278. 



