from Penigent to Kirkby Stephen. 81 



approach to accuracy, as the various limestone deposits oflTer a series of good 

 base lines to which all the distant observations may be referred. But in the 

 remaining part of the ascending series we lose all our lines of verification ; 

 and the sections, as might have been expected, differ very widely in their 

 details. Out of much apparent confusion, we may, however, make out an 

 approximate order, and divide a great thickness of strata into groups suf- 

 ficiently extended to admit of a general comparison among themselves. 



12. Great upper Shale. Thickness varying from 40 or 50 tonearly 200 feet. 

 This group is complex, containing, here and there, a band of croio-limestone, 



and having many subordinate masses of grit, generally of a thin, slaty texture. 

 On the whole, however, it is characterized by a dark-coloured shale, and 

 makes a remarkable feature in the higher parts of many of the mountains, 

 being often laid bare by the deep water-channels which intersect the boggy 

 region between the^rs^ millstone grit and the twelve-fathom limestone. 



On the south side of Baw Fell (in the brow above the marble quarry men- 

 tioned above (p. 79.)), a five-inch coal is, I believe, subordinate to this group ; 

 and, on the west side of the mountain, it contains a strong band of crow-lime- 

 stone. In a part of Swaledale it contains the main chert, Mack beds, red beds, 

 iron beds, &c. enumerated in the detailed sections of the miners in that district. 



13. First Millstone Grit. Thickness varying from 20 to 60 feet. 



The term is here used with considerable latitude, being applied to a group 

 of strata, a part only of which has the true character of millstone grit. When 

 used more strictly, it designates a coarse, open-grained, siliceous gritstone very 

 irregularly bedded, often subdivided by lines not parallel to the planes of stra- 

 tification, and usually containing a considerable quantity of kaolin, and small 

 rounded pieces of opaque quartz interspersed irregularly through its mass. 



The prevailing colour of the group, here described, is light grey ; but this 

 is by no means constant. The characteristic millstone grit is sometimes found 

 associated with all parts of this group ; sometimes only with the upper part ; in 

 which case the lower beds generally consist of a hard, light grey, thin-bedded 

 sandstone. Sometimes the millstone bands are entirely wanting, and then the 

 group (especially when the beds alternate with shale) cannot be easily sepa- 

 rated from that which is next superior to it. 



It is finely exposed in the last precipice of Penigent, and in the strata which 

 form the crown of Ingleborough. It also forms a part of the higher escarp- 

 ment of Whernside and of Great Colm*. 



* The open-grained varieties of gritstone in this group sometimes decompose into a sharp sili- 

 ceous sand, which is much used in the saw-mills where the marble blocks are divided into thin 

 slabs fit for polishing. 



VOL. IV. SECOND SERIES. M 



