526 Correspondence — C. T. A. Gasier. 



granites ; these areas, which are cfuite bare except where covered 

 by occasional clumps of grass, are remarkable in being quite fresh, 

 showing no signs of weathering or any other kind of alteration. The 

 absence of laterite on such surfaces has been explained by Mr, Morrow 

 Campbell, who has paid much attention to the conditions under 

 which rocks become kaolinized and lateritized in the tropics. This 

 writer considers that crystalline rocks mu.st be altered before they 

 can be lateritized, and also that the alteration necessary, generally 

 kaolinization, can be produced only when the rocks have been for 

 a long time continuously in contact with vadose water, i.e. in the 

 zone of permanent saturation.^ Accordingly, the fresh surface rocks 

 referred to above, not having been subjected to such conditions, 

 remain unlateritized. 



F. DiXEY. 



University College, Cardiff. 

 October 4, 1920. 



AN UNDESCEIBED SPECIES OF TROCHILIOPORA. 

 Sir, — I desire to draw attention to a band of Chalk in Sussex, 

 about 10 feet thick, near the base of the zone of Micraster cor- 

 anguinmn, in which an undescribed Polyzoon belonging to the genus 

 Trochiliopora is very common. As this fossil appears to be confined 

 to the said band of Chalk, and also owing to its abundance, it has 

 proved to be a very useful local zonal guide fossil. The exact 

 position in which it occurs in the Micraster coranguinum zone is as 

 follows : — 



Lower fourth rStrong 31. coranguinum tabular flint band. 



of zone of | Chalk, about 3.5 feet. 



Micraster "| Chalk with Trochiliopora sp., 10 feet. 

 coranguinum. IChalk, about 17 feet. 

 Chalk of zone of Micraster cortestudinarium. 



I propose to call the 10 feet of chalk referred to " the Trochilio- 

 pora bed ". 



The genus Trochiliopora has been described by Professor J. W. 

 Gregory in the Geological Magazine, 1909, p. 65, and also in the 

 British Museum Catalogue of Cretaceous Bryozoa, vol. ii, p. 265. 

 The species above referred to resembles T. humei, Gregory, but its 

 body tapers to a much finer stem than the stout blunt stem of the 

 latter species. 



The Trochiliopora bed is rich is Polyzoa, it having yielded some 

 rare and interesting forms. 



Christopher T. A. Gaster. 



Lewes, Sussex. 

 October 4, 1920. 



GEOLOGY OF THE NINGI HILLS. 



Sir, — Major Williams' paper on the geology of the Ningi Hills 

 of Nigeria in the October number is very welcome. It indicates not 

 ^ Morrow Campbell, op. cit., p. 123. 



