HISTORY OF GRITS AND SANDSTONES. 



27 



Tho above facts would appear to render it probable that the 

 rounded grains of these sandstones may bo of seolian origin, and 

 that, during certain periods of Triassic time, desert areas with blown 

 sands extensively prevailed in this country. 



Mr. De Ranee has observed that the millet-seed beds are usually 

 free from pebbles, shale-beds, pseudomorphs after common salt, and 

 from all traces of life* — conditions which are characteristic of de- 

 posits produced by wind- currents. 



The granules of brown iron-ore which are so plentiful in the 

 " Carstones " of Hunstanton are pisolitic grains, and not fragments 

 of that mineral rounded by attrition. 



An instructive example of the occurrence at the same time of 

 rounded and angular grains is met with in the Interglacial sands of 

 Flintshire, where some of the pebbles are fragments of a millet- 

 seed sandstone, while many of the smaller particles are grains 

 detached from the same rock. . 



EXPLANATION OF PLATES I. & II. 



Plate I. 



Magnified 18 diameters. 



Fig, 1. Group of felspar crystals in Cambrian Grit. Polarized light: p. 7. 

 2. Grit from Ladock, Cornwall, enclosing a fragment of a volcanic rock. 

 Polarized light : p. 10. 



Plate II. 



Magnified 100 diameters. 



Figs. 1, 2, 3, & 5. Crystals of quartz deposited upon rounded grains of the same 

 mineral in Bunter Sandstone : p. 13. 

 4. Depression in a grain of quartz from the same sandstone. 



6. Corroded grain of felspar from the same. 



7. Rounded grain of quartz with attached crystal of iron pyrites. 



Discussion. 



The President expressed his sense of the value of Mr. Phillips's 

 communication. 



Dr. Sorby expressed his agreement with the paper, to which he 

 had listened with great interest, especially as the author had ap- 

 proached the subject from a point of view somewhat different from 

 his own. He was especially glad to find that his opinions were 

 confirmed by the author, especially as to the crystals of quartz in 

 certain sandstones. The observations as to the time required to wear 

 down a grain of sand were especially valuable- He had found the 

 drift sands of the Yorkshire coast almost all angular ; but then those 

 examined by Mr. Phillips were from another locality, which might 

 explain the difference in their observations. He should only regard 

 sand as aeolian when a very large proportion of grains were rounded. 



* "Further Notes of Triassic Borings near Warrington," read before the 

 Manchester Geol. Soc. June 29th, 1880. 



