Geological Society. 233 



(3) Kundt's tube, ^- equals 105 millims. The glass reso- 

 nators of the acoustic mill were of the form D (fig. 1) : a b 

 equalled 24 ; hf,2; fg, 7 ; length of the arms 30 millims. 



It is a striking fact that very small resonators may give a 

 very deep note : with fork A, I used a glass resonator of the 

 form D (fig. 1), in which a b equalled 24, lif 14, and fg 1 

 millim. The volume was about ninety times less than that of 

 the resonant box of the fork, to whose note the resonator was 

 tuned. Notwithstanding its smallness it showed acoustic re- 

 pulsion. 



XXX. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 153.] 



•June 5, 1878.— John Evans, Esq., D.C.L., F.K.S., Yice- President, 



in the Chair. 

 T^HE following communications were read: — 

 -*• 1. " On the Quartzites of Shropshire." By Charles Callawaj^, 

 Esq., M.A., B.Sc, F.G.8. 



In a former paper (Q,. J. G. S. xxxiii. p. 652) the author indicated 

 that part of the so-called quartzites of the "Wrekin are " Hollybush 

 Sandstone ;" in the j>resent communication he shows that the 

 whole, both in the Wrekin and Church- Stretton areas, are of Cam- 

 brian or Precambrian and not of Caradoc age. 



In the "Wrekin area the quartzites rest unconformably against the 

 volcanic axis in a nearly continuous band, dipping away from it at 

 angles of from 30 c to 55°, their present position being due to its 

 elevation. The volcanic rock is a bedded Precambrian tuff, which 

 reappears in Lawrence Hill and the Ercal, also accompanied by 

 quartzites overlain by Hollybush Sandstone. Caer Caradoc belongs 

 to the same volcanic series ; and the quartzites reappear on its S.E. 

 flank, overlain by Hollybush Sandstone containing Kutorgina cin- 

 gulata and Serpidites fistula, above which follow the Shineton Shales, 

 and next, separated by a fault, the Hoar-Edge grits (Lower Caradoc). 

 The author believes that the apparently conformable succession here 

 is due to parallel faults. Along the S.E. flank of the Wrekin the 

 quartz rock dips S.E., while the volcanic rocks dip N., and fragments 

 of the latter are contained in its base. The author is inclined to 

 consider this a friction-breccia, and the junction a faulted one. He 

 also regards the junction with the Holly busk Sandstones as a faulted 

 one, and maintains that in any case the quartzites are older than the 

 latter rocks, which are sometimes considered the equivalents of the 

 Ffestiniog group, and by Mr. Belt to be Menevian. The quartzites 

 can hardly belong to any part of the Upper Cambrian ; and the 

 author passes on to consider the various positions which they may 

 be held to occupy, and gives reasons for thinking that they are Pre- 



