708 KEPORT— 1892. 



by the author in Anglesey ; at Liverpool, Garston, and Hale Head in Lancashire, 

 and at Dawlpool and Birkenhead in Cheshire. The liev. Mr. Barker, S.J., has 

 recorded it from the Vale of Clwyd. 



It is always accompanied by South Scottish granites, and where these pre- 

 dominate, as in the Isle of Man, it is common. About Liverpool the Scotch rocks 

 are about in the same proportion as those of Lake District origin, and further east 

 the Scotch cease altogether. 



Floating ice could not have transported the Ailsa Craig and other northern 

 rocks, as there is not a free intermingling of types. There is also a vertical uplift 

 of over 200 feet from Ailsa Craig (1,140 feet) to Moel-y-Tryfaen (1,350 feet). The 

 ridge of which Moel-y-Tryfaen forms a part acted as a barrier, and destroyed the 

 force of the Snowdonian ice northwards, and thus tlie northern ice got the mastery 

 and pushed the northern erratics up to the summit of Moel-y-Tryfaen. 



3. Report of the Committee on Erratic Blocks, — See Reports, p. 2G7. 



4. The Cause of the Ice Aqt. 

 By J. W. Gray, F.O.S., and Percy F. Kendall, F.G.S. 



Two hypotheses at present engage the attention of glacialists, viz., a, that 

 propounded by CroU, which ascribes the glacial cold to the combined effects of a 

 liigh degree of eccentricity of the earth's orbit and the precession of the equino.xes, 

 with, as secondary causes, changes in the winds and marine currents ; and b, the 

 explanation presented in detail by Mr. Warren Upham, which is based upon great 

 earth-movements which might lift wide areas above the snow-line. 



Neither of these appears to satisfy the known geological conditions, which may 

 be defined as follows : (1) The Glacial period was a unique episode, no evidence 

 being adducible of any previous Glacial period, but only of glacial conditions in 

 the neighbourhood of mountains. (2) The cold conditions came on witli extreme 

 •slowness, the refrigeration being progressive from the Eocene period to the climax. 

 (3) The Glacial period was of long duration, judging by the great dimensions of 

 the glaciers and the amount of work done by them. (4) The return to temperate 

 conditions was very rapid. (5) The final disappearance of the ice was a very 

 recent event; the condition of the drift accumulations and direct measurements 

 .such as those of the recession of waterfalls point to a maximum of 10,000 years. 



OroU's hypothesis, in the opinion of the authors, is in opposition to Nos. I, 2, 

 4, and 5. 



Upham's explanation has much to commend it. Submerged valleys of com- 

 paratively recent date exist upon many coasts, e.y., one which deeply indents the 

 1,000-fathom line at the mouth of the Congo; but the rate of filling up of these 

 gulfs is not known, and they are not necessarily even approximately contem- 

 poraneous. 



Arguments against this explanation may also be drawn from Nos. 1, 2, 4, 

 and b. Any explanation must apply to Britain, but the indications of cold con- 

 ditions in Pliocene times, when the sea reached British shores in East Anglia, 

 Cornwall, and Aberdeen, are inexplicable on this hypothesis. Furthermore, the 

 sea-level was not appreciably lower in Caithness, Aberdeen, the Firth of Clyde, 

 and the Irish Sea at a time when glacial conditions of great .severity had set in ; 

 and in Yorkshire, when the Scandinavian glacier approached the coast, the land 

 stood at the same level as at present. 



The authors formulate no hypothesis, but they consider that the causes are to be 

 sought outside the earth ; and, having regard to the uniqueness of the Glacial period, 

 its recency and its very gradual oncoming, they think it may be connected with a 

 secular cooling of the sun. The great development of sun-spots must affect the 

 radiating power of the sun, and the sudden blazing out of novce shows that causes 

 are in operation which are adequate to produce a temporary rejuvenescence of suns. 



The authors ask the aid of astronomers and physicists in the solution of one 

 of the unsolved problems of geology. 



