1869.] WARD — KNAEESBOROTJaH GRITS. 295 



sandstones generally supposed to be Permian, occurring along the 

 eastern edge of the Yorkshire coal-field immediately below the mag- 

 nesian limestone. 



The first of these two points in favour of a Permian age can go 

 for little, inasmuch as grits and conglomerates of all ages are likely 

 to resemble one another in structure. The second point, however, 

 deserves more consideration, and mainly for two reasons : — 



1st. That the purple tint is unusual among millstone -grit beds 

 proper. 



2nd. That this is the tint generally assumed by the so-eaUed 

 " Lower-Eed-Sandstone " beds immediately beneath the magnesian 

 limestone. 



Eed gTits, as stated before, are not unfrequent in the millstone - 

 grit series ; thus, in a section of a bore -hole made on Bradford Moor, 

 the rough rock is termed "Red Sandstone," and in another case 

 " Old Red Sandstone ; " while in several parts of the Yorkshire 

 miUstone-grit area between the Lancashire and Yorkshire coal-fields, 

 various members of the grit have in places a red colour. The pur- 

 ple tint, however, is rarely, if ever, met with in large masses. In 

 one spot only, far removed from the limestone, have I ever observed 

 it ; this was in a shaly band occurring among Third-Grit sandstones, 

 three miles north of Leeds, and five west of the limestone escarp- 

 ment, on the turnpike road between High Moor Allerton and Hill 

 Top, the nearest limestone outlier being distant three miles. 



On the other hand, the purple colour of the Plumpton grit is by 

 no means constant ; thus a little north-east of Spofforth, on the road 

 to JSTorth Deighton, the magnesian limestone in Newsome-Bridge 

 Quarry is seen Ijing upon a very uneven surface of whitish grit with 

 no trace of red or purple coloration ; while but one-eighth of a mile 

 distant, in St. Helen's Quarry, the grit is coarse and purple, and has 

 lying upon its denuded surface a bed of red marl, at the thickest 

 part five feet, and overlapped towards either end of the quarry by 

 yellow limestone ; the marl contains in one part a thin layer of ap- 

 parently redeposited grit. I would here also observe that the lower 

 part of the limestone, wherever it rests on grit, is apt very frequently 

 to contain fragments of the latter or scattered quartz-pebbles. 



As the result of my observations in general, I should infer that 

 the frequent red and especially purple colour of beds immediately 

 underlying the magnesian limestone is due in some way or other to 

 the limestone covering, and its former extension further to the west. 

 The coloration, I should presume, is chiefly due to the peroxidation 

 of iron ; and this, it seems to me, may take place in two ways — either 

 by the action of carbonated water from the limestone above filtering 

 through porous grits and sandstones, and converting the protoxides 

 contained in them into sesquioxides, or by iron being brought from 

 the overlying limestone, in the form of hydrate and carbonate, and 

 redeposited in the rocks below. 



Prof. Sedgwick says, in the same article before quoted, that 

 " hydrate of iron appears to form the colouring-matter of many of 

 the yellow beds of limestone, also of many of the beds of marl and 



