1851.] SEDGWICK PALEOZOIC ROCKS OF WESTMORELAND. 45 



(2.) At Thornton Force* are some traces of calcareous conglome- 

 rates immediately under, and partly penetrating, the bottom beds of 

 limestone. They seem to represent the old-red-sandstone in a very 

 degenerate form ; and they disappear in some of the neighbouring 

 sections. Indeed, throughout the North of England, the old-red- 

 sandstone, even when developed on a far greater scale, is generally 

 seen in discontinuous masses. 



(3.) Next we have a series of beds (figs. 3 and 4, e) rising from 

 beneath the terrace of limestone and conglomerate, and composed of 

 hard gritty greywacke (provincially called calUard), alternating in- 

 definitely with slaty and flaggy beds, which show, here and there, 

 traces of transverse cleavage-planes. The dip is south-westerly and 

 at a high angle ; and near the end of the group the beds become 

 almost vertical, and so fissile, that large slate-quarries have been 

 opened in them. The quarries on the Thornton Beck section are 

 spoiled by joints and fractures, and are now deserted ; but the quar- 

 ries on both sides of the other rivulet (Ingleton Beck) are still 

 worked extensively. The slates are coarser than the fine greenish-blue 

 slates of the central group of Cumberland, but resemble them in co- 

 lour. Some of them are marked with beautiful dendritic coverings 

 of pyrites, and occasionally studded with large bright cubes of that 

 mineral. Good sound roofing-slates are, however, obtained without 

 any taint from pyrites. The slaty planes are vertical, and exactly 

 parallel to hard beds of calliard which rise at their side ; and hence 

 it follows that the planes of fission are parallel to the original laminse 

 of deposit. But as these Ingleton slates are sometimes marked by 

 numerous parallel stripes or striae, I at first concluded that these 

 stripes must represent the lines of deposit, while the great fissile 

 planes represented a regular transverse and nearly vertical cleavage. ' 

 In this I was, however, mistaken. In these slates the great smooth 

 planes, from which the rock derives its value, are parallel to the 

 bedding ; and the stripes upon these slaty planes represent the inter- 

 section of a true system of transverse cleavage-planes. I never re- 

 member to have seen any structure like this in the old quarries of 

 North Wales, Westmoreland, or Cumberland ; but I have seen some 

 parallel instances in Devonshire and Cornwall. Taking all the series 

 above-described as a group, and judging of it only by its mineral 

 character, its hardness, and above all by its prevailing chloritic tint, 

 I should not have hesitated in classing it, provisionally, with some 

 of the coarser slates, in the central group of Cumberland, under the 

 Coniston limestone. 



(4.) Further down the two rivulets, and overlying the rock of the 

 slate-quarries, are some coarser and less fissile beds (figs. 3 and 4, d). 

 At a very short distance they become slightly puckered by an inter- 

 mixture of very irregular calcareous concretions, and it deserves re- 

 mark, that these calcareous and very irregular portions are chiefly 

 arranged upon ill-defined cleavage- planes, and not generally on the 



* A pictorial representation of Thornton Force is given in Phillips's Geol. York- 

 shire, pi. 23. 



