M. M. Beeley — Disturbed Gravels. 157 



photographs of Plate XI, gives visual proof that the same course was 

 followed as in the artificial melt. It should, however, be mentioned 

 that part of the soda-lime felspar probably enters into the crystal 

 framework of the augite, while another part may remain hidden in 

 the residual glass. The presence of a minute reaction rim of biotite 

 between olivine and the glass further suggests that the latter may 

 contain the constituents of orthoclase. Consequently the actual 

 amount of felspar in the rock is less than that calculated from the 

 analysis, while the pyroxene appears to be correspondingly more 

 abundant. 



In conclusion, I wish to express my thanks to Dr. H. F. Harwood 

 for his collaboration in making the analysis, and to Mr. Gr. S. 

 Sweeting for taking the micro-photograpns with which the paper is 

 illustrated. 



EXPLANATION OF PLATE XL 



FlG. 1. — Picrite from the Ampwihi Eiver, Mozambique. Corroded phenocrysts 

 of olivine, serpentinized along cracks, are seen in a fine-grained 

 groundmass. x 25 diameters. 

 ,, 2. — Groundmass of picrite from the Ampwihi River, showing grains of 

 augite lying amongst parallel or radiating laths of labradorite. 

 In places the two minerals show graphic intergrowth. On the right- 

 hand side a rounded crystal of enstatite of earlier crystallization 

 than the rest of the groundmass can be seen, x 125 diameters. 



IV. DlSTCKBED GEAVKLS. 



By E. M. Deeley, M.Inst. C.E., F.G.S. 



THERE are many features characterizing the surface portions of 

 deposits which are very puzzling. Indeed, the more one studies 

 them the less one is inclined to be dogmatic. Many true glacial 

 deposits show remarkable signs of disturbance throughout their mass. 

 "We may instance the Contorted Clay of Norfolk as a case in point. 

 Even when boulder-clays are too uniform in texture to show signs of 

 movement they are often kneaded into the rocks upon which they rest, 

 and rocks of all ages often show such disturbances when they have 

 been overridden by ice. Here we are dealing with the results 

 produced by the action of forces operating from without the deposit. 



In other cases, as I have attempted to show, 1 the effects can be 

 accounted for in the supposition that we have heavy beds of gravel 

 or gravelly clay sinking into soft lighter clays or marls below. The 

 trail and underplight of Spurrel seems to be caused by such movements. 



There are disturbances, however, which it seems to be impossible 

 to account for in this way. I refer to the peculiar signs of 

 movement shown by gravelly and sandy deposits, even when they lie 

 outside the areas which we know to have once been covered by ice- 

 sheets. They are to be seen in many of the gravels and sands of the 

 ■South of England, and also in river gravels, which there is reason to 



1 Geol. Mag., 1916, pp. 2-5. 



