284 Reports dc Proceedings — Geologists' Association. 



Geologists' Association. — May 7, 1920. 



"Implements from Plateau Brick-earth at Ipswich." By 

 Eeginald A. Smith, F.S.A. 



On the east side of Ipswich, immediately east of Derby Road 

 Station, extensive excavations for brick-earth have brought to light 

 a fine series of flint implements now^ in Miss Layard's collection at 

 Christchurch Mansion, and described in Journ. R. Anthrop. Inst., 

 xxxiii, 41 ; xxxiv, 30G ; xxxvi, 233. With the assistance of the Percy 

 Sladen Trust, a large pit was dug under careful supervision in 1914, 

 and the occurrence of worked flints at different levels verified. 

 There had been 2 feet of contorted gravel above, and a sloping bank 

 of gravel below, a wedge of brick-earth, suggesting the former 

 presence of a river, w^hich can, indeed, be deduced from the levels. 

 Clement Reid recognized Boulder-clay at the bottom of a boring, 

 at 27 feet, and the geology of the site has been studied by Professor 

 Boswell (Proc. Geol. Assoc, xxv, 135), but a comparison with the 

 Caddington Series {Archeologia, Ixvii, 49) strengthens the argument 

 for plateau deposits late in the palaeolithic Drift period, and reopens 

 the question of their relation to the Terrace gravels. The site is on 

 an isolated part of the plateau between the main and lateral valleys 

 of the Gipping and Deben, and is 120 feet above sea-level, the 

 Boulder-clay terminating in an east-and-west line 1 mile to 

 the north. 



Optical Society. — April 15, 1920. 



" The Rock Crystal of Brazil." • By R. R, Walls, M.A., B.Sc. 



The author describes the occurrence in the field of the clear variety 

 of quartz known as rock crystal. Although the high plateau of S.E. 

 Brazil is essentially a granite and gneiss country, the rock crystal 

 is not found in the granite itself, but in a series of bedded quartzites 

 overlying the granite. Clear rock crystals occur only in the spaces 

 between the bedding planes, but the planes of the crystals can be 

 traced downwards for several feet across the bedding planes. Huge 

 crystals have thus been formed, and the author illustrated one 

 weighing 13 cwt. Clear crystal and coloured varieties — amethyst,, 

 smoky, and cairngorm — were found according to the purity or 

 impurity of the original sandstone. 



The sandstone had evidently been " stewed up " and metamor- 

 phosed into " crystal ", but what was the cause of this is not clear. 

 Intrusive granite suggested itself, but there was no sign of it any- 

 where. The crystal was found often in the neighbourhood of 

 sericitic schist, which when worked out seemed to occupy a fissure 

 in the horizontally bedded sandstones and quartzites. The sericitic 

 schist contained diamonds, but w^as very evidently not an alluvial 

 deposit. It appeared, therefore, as if this schist was the highly 

 metamorphosed remains of a volcanic pipe similar to the diamond- 

 bearing pipes of South Africa, and that its intrusion into the sand- 

 stones and quartzites had metamorphosed the latter into "crystal"^ 



