336 ME. T. H. J3UET0]!i OX THE MICROSCOPIC [vol. Ixxiii, 



naineh" : sandstone, limestone, and chert, have probably been derived 

 from the Pennine ridge, it is reasonable to infer that a small pro- 

 portion of the heav}'^ minerals are also from the same source. 

 Subordinate currents i have also evidently contributed their quota 

 to help to form the Pebble-Eeds. 



It appears, therefore, that Scotland has furnished the bulk of 

 the staurolite, and of the other heavy minerals associated with it. 

 Tourmaline too, at any rate in greater part, is from northern 

 sources. 



How, then, did the foregoing m^inerals reach Nottinghamshire ? 

 To answer this question, it is necessary to compare the material of 

 certain other localities with that under consideration. 



The heavy minerals of Cannock Chase, Nottinghamshire, and 

 Cheshire Pebble-Bed sand that I have examined, are substantially 

 identical. They exhibit, on the whole, a marked difference from 

 those of the South Pennine district (see Synopsis, pp. 334-35). 



Slices of quartz-felspar grits from the Pebble-Beds of Nottingham- 

 shu'e and Cannock Chase, also from Loch Torridon, show a striking 

 resemblance one to the other, both macroscopicalh^ and microsco- 

 pically. They are mainly composed of quai'tz and felspar, with an 

 addition of quartzite, pegmatite, and microcline.^ The similarity of 

 the Nottinghamshire material to that of Cannock Chase suggests 

 a common source of supph^ 



To the more numerous and distinctive rocks of the Pebble-Beds 

 of the Midland Bunter, Prof. Bonney ascribes a noi-thern de- 

 rivation '^ : a north-western river and its tributaries being the 

 means of transport. This north-western river has probabl}^ played 

 an important part in the formation of the Nottinghamshire Pebble- 

 Beds. At certain flood-periods, when the supposed river Avas much 

 fuller than usual, and its outlet and the approaches thereto were 

 probabh^ more or less obstructed by material brought down 

 previously,* an overflow occurred. This was probably in the 

 neighbourhood of Macclesfield. The flood-water, with its load 

 of sediment, forced its w^ay across the high land of Derb3^shire 

 into Nottinghamshire and the lower-lying lands of the east.^ 



The main current of the overflow postulated above, when it 

 reached Nottinghamshire, bifurcated in the Gorsethorpe district, 

 one brancli flowing mainly eastwards by way of the Ollerton 

 district, and the other south-eastwards by way of Farnsfield. 



^ 'The Geology of the Country around Ollerton' Mem. Geol. Surv. 1911, 

 p. 22. 



2 'The Geological Structure of the N.W. Highlands of Scotland' Mem. 

 Geol. Surv. 1907. p. 28-5. 



'■^ Q. J. G. S. vol. Ivi (1900) p. 302. 



-* The staurolite of Nottinghamshire is fresher than the staurolite of Can- 

 nock Chase and that of Cheshire : this lends support to-the above-postulated 

 theory of obstruction. The material in the first instance (long accumulated 

 and weathered) was brought down by the flood- water into the western basin, 

 naturally more or less blocked later, and certain fresher material was similarly 

 brought from the north — much of the latter being carried by the overflow 

 into Nottinghamshire and the eastern lowlands. 



^ A. J. Jukes-Bro^vne, ' Building of the British Isles ' 3rd ed. (1911) p. 235. 



