Geological Society of London. 89 



about the same throughout, because the angle at which matter will 

 •stand depends partly on gravity and partly on friction. Now, as 

 long as the water is at rest, the equilibrium in water remains as in 

 air ; but as soon as the water is agitated, the friction is diminished, 

 and the angle of repose becomes less. In other words, the pebbles 

 are set iii motion, and roll down the hill. 



This explains the equal width of the roads, because the new angle 

 of repose being equal througliout, and the depth to which the agita- 

 tion extends being also equal, the width of the road must be equal 

 also ; and when once the new slope of repose was acquired, the 

 hill-side would again be in a condition of equilibrium, and the road 

 would receive no further enlargement, however long the water might 

 stand at the same level. This explains why there are no roads 

 when the natural rock appears, or when the hill-side is less steep 

 than usual ; whereas, if the roads were due to a heaping-up action, 

 of course in places where the sides were more shelving the roads 

 would be better marked. We can also thus understand why there 

 are no rolled pebbles on the roads ; and lastly, as the lower line of 

 the roads marks the depth to which the water was disturbed, we can 

 see why the roads become narrower wherever they are steeper than 

 usual. 



Finally, the vertical height of the roads — that is to say, the 

 vertical difference between their upper and lower lines — gives the 

 measure of the depth to which the water filling the valleys was 

 agitated, and affords thus an additional argument in favour of its 

 having been that of a lake, as in a tidal sea the width of the roads 

 must have been much greater than it is. 



2. " Remarks on the Geological Features of the Northern part of 

 Formosa and the adjacent Islands." By Cuthbert CoUingwood, 

 M.B., F.L.S. Communicated by the Assistant-Secretary. 



The west coast of Formosa is flat, consisting of low alluvial 

 plains, with a few hills, some of which approach the coast ; a range 

 of mountains runs nearly through the island. Near Tamsuy, on the 

 right bank of the river, is a thick deposit of clay, containing boulders 

 on which the author could detect no traces of glacial strise. Higher 

 up the river, on the north side, hills containing sulphur-springs rise 

 from the plain. On the north-east side of the island sandstone 

 extends from Masou peninsula, north of Kelung, to Petou Point on 

 the south-east. The harbour of Kelung is a spacious excavation in 

 the sandstone, which is hollowed out into numerous caves ; and Dr. 

 CoUingwood states that the land is slowly rising, blocks of water- 

 worn coral being found above high-water mark. Sano Bay, the 

 only harbour on the east coast, is protected by a reef composed of 

 trap-rock. The Pescadores are of volcanic origin, and are composed 

 of basalt. The author then describes Hai-tan, and the islands of 

 Craig and Agincourt, which lie to the north of Formosa, as well as 

 the Pinnacle Islands, lying still further north. 



3. "On some Sources of Coal in the Eastern Hemisphere." By 

 Cuthbert CoUingwood, M.B., F.L.S. 



1. Kelung, Formosa. —The coal is found in depressions in Eed Sand- 



