308 J. V. Ehden — Origin of Pegmatite Veins. 



found by us in the same beds at Instow quite recently. These, 

 and two fish-remains from Instow, Coslacanthus elegans, Newb., 

 and Elonichihys Aitkeni, Traq., also in the British Museum ' are 

 practically all the determinations, with the exception of plant- 

 remains, which have so far been made from the Upper Culm 

 Measures of Devon. 



In conclusion, we believe that the calcareous nodules and the 

 limestone of the Clovelly district belong to a much higher horizon 

 in the Upper Culm Measures than the Instow beds. Whether the 

 nodules, now found in a number of scattered localities in the former, 

 are really confined to a single bed, or occur on different, but not 

 distant, horizons, we are unable to ascertain, as the severe folding, 

 faulting, and crushing which the rocks have undergone render it 

 rarely possible to trace any bed for more than a few yards. At 

 any rate, the occasional occuiTence of calcareous nodular beds seems 

 to be in some measure characteristic of the Culm Measures of the 

 Clovelly district. 



It would seem that, in Devonshire, marine Cephalopoda such as 

 Gastrioceras carhonarium, which are usually regarded as more 

 restricted vertically than other pabeontological types, have a con- 

 siderable range in the Upper Culm Measures, occurring in what 

 are probably the lowest and highest beds of that series. It may 

 be also pointed out that the occasional occurrence of marine calcareous 

 bands is an important point of agreement between the Upper Culm 

 Measures and the Coal-measures of other British coalfields, more 

 especially those of North Staffordshire ^ and South Lancashire.-' 



V. — On the Origin of certain Pegmatite Veins. 

 By J. YixcEXT Elsden, B.Sc, F.G.S. 



DURING a visit to the South of Sweden in the Summer of 1902 

 I noticed the frequent occurrence in granite of pegmatite veins 

 showing a succession of small but veiy regular foldings, which, 

 howevei', did not affect the parent rock. In sett quarries where 

 these folded veins existed the rift of the rock was perfectly regular 

 on each side of the pegmatite, proving conclusively to my mind that 

 the contortion of the veins took place prior to the consolidation of 

 the main mass. The granite of this district occupies a wide area, 

 and possesses a very uniform mineralogical constitution, although it 

 varies much in texture between a rather coarse-grained granitite 

 and a fine-grained, compact, gneissose rock possessing well-marked 

 foliation. The pegmatite veins are fairly numerous, but are generally 

 rather insignificant in vpidth, occasionally thinning out to mere 

 streaks not more than a few inches in thickness. 



The origin of pegmatite veins has been much discussed, but most 

 of the various theories hitherto advanced almost invariably attribute 



1 Eegistered numbers P. 6100, P. 5379, and P. 6268. 

 - Ward: Geol. Mag., Vol. II (1865), pp. 234 and 286. 



3 Hull & Green, Trans. Manch. Geol. Soc, vol. iii (1862), p. 348; and Hull & 

 Salter, " Geology of the Country round Oldham," 1864, p. 64. 



