Correspondence — Mrs. J. Longstaff. 329 



form of the intrusion, in the presence of a curved, flanking fault, 

 and in the shearing of early consolidated parts of the mass. 



The dykes point to the operation of regional tensional stresses 

 which, co-operating with the pressure of the magma, opened parallel 

 north-north-east and south-south-west fissures. It is suggested that 

 the concentration of the dykes was due to the pasty condition of the 

 internal parts of the granite mass, which yielded to the stresses and 

 caused a localization of fissures in the surrounding solid rocks. 



After the intrusion of the majority of the dykes, a further subsidence 

 within the Cruachan granite mass admitted the central core of the 

 Starav granite. 



The principle underlying the interpretation of the phenomena 

 described is the upward movement of igneous magmas in correlation 

 with complementary subsidence of portions of the earth's crust. 



2. "The Pitting of Flint Surfaces." By Cecil Carus-Wilson, 

 F.E.S.E., F.G.S. 



Regular pittings of uniform size are occasionally seen on fiints 

 which have been exposed to the weather. They have been referred 

 to by various authors, but no satisfactory explanation of their origin 

 has been given. The author procured some interesting examples 

 occurring in a recent deposit near Folkestone. This deposit is formed 

 of materials which appear to have been washed down from the 

 adjacent chalk hills. The flints appear to have been derived from 

 the sandpipes in the Chalk : their surfaces are much decomposed. 

 The removal of the colloid silica has rendered them very porous, and 

 they absorb a good deal of water. It is believed that the pittings are 

 due to mechanical action. Observations and experiments carried out 

 by the author indicate that sucli markings cannot have been produced 

 by blows, nor by any process of desiccation, and that the freezing of 

 the absorbed water seems to be the only satisfactory explanation to 

 account for the various details of the phenomenon. 



COI?.I?.ES]POISriDElSrCE!- 



THE GENOTYPE OF LOXOXEMA, PIIILL. 



Sir, — About a week after the publication of the Quart. Journ. Geol. 

 Soc, vol. Ixv, pt. ii. May, containing in full my paper on the genus 

 Loxo7iema, read on January 13, I received vol. viii of Essais de 

 PaUoconchoIogie Comparee, by M. Cossmann, published in April, but 

 apparently only distributed in June. 



It IS impossible to bestow adecpate praise on this admirable and 

 laborious Avork, and I feel sorry to be obliged to differ on any point 

 from its learned author. Nevertheless, I have unwittingly taken 

 a different view with regard to the genotype of Loxonema, and 

 I consider it advisable to give my reasons for so doing in greater 

 detail. More especially do I feel the need of tliis since I also at 

 first was in accord with M. Cossmann in taking the Devonian form 

 erroneously described by Phillips as L. simiosum (Sow.) for genotype 

 (Quart. Journ. Geol. Soc, 1905, vol. Ixi, p. 564). Further investi- 

 gation, however, has convinced me that the Silurian L. sinuosiim, 

 described by Sowerby as Terehra'i sinuosa (Sil. Syst., p. 619, and 



