28 ON THE CONSTITUTION AND HISTOliY OF GRITS AND SANDSTONES. 



So far as his observation had gone, the sands of the dunes on our 

 coasts were not much more rounded than other sands. 



Dr. Hicks said that the condition of the Barmouth Grit led him to 

 think that the materials had not drifted from far. He had also 

 observed that there was a large proportion of rounded grains in 

 the Stiper Stones ; were we to suppose these to be blown sands ? 

 Rounded grains were still more common in the quartzites of the 

 ]S".W. of Scotland ; we must believe therefore that there was, still 

 remaining at the time they were deposited, an adjoining great land- 

 area or the materials from one not far away. 



Mr. De Bance said that the Keuper beds under the Marls were 

 now divided into the Water-stones, soft current-bedded sandstones 

 called Erodsham beds (which denoted entirely different physical 

 conditions and contained the millet-seed grains), and then the Lower 

 Keuper building-stone (Labyrinthodoii-be&s). Then came a line of 

 erosion. In the Bunter series were the Upper Mottled Sandstones 

 (with the millet-seed grains), then the Pebble Beds (which had a 

 different kind of current-bedding from that of the Erodsham beds), 

 then another line of erosion and the Lower Mottled Sandstone with 

 millet-seed grains again. The bedding of the sandhills of Lanca- 

 shire much resembled that of the Erodsham and other millet-seed 

 beds in their high angle and rapid change. 



Mr. Rtjtlet said he had examined eruptive rocks rather than 

 sedimentary, but could not but express his gratification at the 

 agreement between two such observers as Dr. Sorby and Mr. 

 Phillips. He called attention to the presence of felspar in many of 

 the sandstones described, and suggested that it was possible for 

 such sandstones to be changed into f els tone. There was often 

 much difficulty in distinguishing between the finer-grained igneous 

 and sedimentary rocks. He also called attention to the develop- 

 ment of microcrystalline structure in felspar crystals. 



Mr. Blanfoed said that some years ago he had examined the 

 Indian desert, and found the grains of sand well rounded. They 

 were mostly of quartz, with a few of felspar and occasionally of 

 hornblende. The strongest wind there blows from the west ; the 

 sands had come from the coast and the river Indus ; and the sand 

 in the bed of the river was also rounded. The blown sand ap- 

 peared unstratified. 



Mr. Phillips said that the grains of millet-seed sandstone were 

 much more rounded than was usual in sea-sand. He thought the 

 rounding of felspar was often due to disintegration by decomposition. 

 With regard to Mr. Blan ford's remarks, he could only say that he 

 believed the grains of all the desert-sands which had been yet 

 examined had been found to be much rounded. 



