28 



KNOWLEDGE. 



January, 1911. 



Reef Problem, explains the phenomena of coral islands as 

 being due neither to crustal subsidence nor to elevation of 

 volcanic islands^ but to changes in the sea-level itself. 

 These changes, broadly treated, consisted in a lowering of the 

 water-le\el, followed by a return to normal conditions as the 

 great ice-caps first grew to enormous dimensions, and then 

 retreated during the Great Ice Age. Estimating the Polar 

 ice-caps during the glacial epoch at an area of six million 

 square miles, with an average thickness of three thousand to fi\e 

 thousand feet, the author points out that the removal of this 

 water would of itself lower the general sea-level by one hundred 

 and twenty-five to two hundred and eight feet (say twenty to 

 thirty-five fathoms). Besides this, however, the gravita- 

 tional attraction of this great mass of ice would heap up 

 the ocean water nearest it to such an extent as to lower the 

 equatorial sea-level another five to eight fathoms. Thus the 

 total lowering of sea-level in the tropics would be (|nite thirty 

 fathoms. Conversely, the deglaciation of the wliolc ice-cap 

 would raise it to this extent. 



Now. the submarine plateaux on which coral reefs are found 

 do not, as a rule, depart very much from an average of about 

 thirty-fi\e fathoms below present sea-level. Allowing for a 

 "veneer" of coral detritus, etc., of ten to fifteen fathoms in 

 thickness, the " solid rock " is about forty-five to fifty fathoms 

 under water. The uniform ity of the plateau level is explained 

 by neither Darwin's nor Murray's hypothesis: the present 

 author explains it as being due to marine abrasion during the 

 Glacial Period. Allowing for the thirty fathom lowering of 

 sea-level produced by the Polar accumulation of ice, this 

 platform would then be within fifteen to twenty fathoms of 

 the surface, a depth in whicli the iiroictli uf the earal 

 organism is possible. 



If the whole earth were chilled during the Glacial epoch (as 

 supposed by some) reef"building corals would be vastly 

 restricted in areal distribution. A fall of six degrees only 

 would enormously diminish the area where the marine 

 isotherms never fall below 20° C, the temperature necessary 

 to coral life. This would mean that most of the present 

 areas of coral seas were then free from such life. As the 

 retreating waters caused low Pleistocene islands to emerge 

 from the sea and no coral fringes protected the loose volcanic 

 or calcareous material, denudation would be very rapid. 

 Exposed on all sides to abrasion by the open sea, these islands 

 would lose substance at least as fast as the chalk cliffs at 

 Dover are doing (about three and a half feet per annum). At 

 this rate the Chagos Bank, now a huge plateau, sixty miles 

 broad by ninety miles long, could have been reduced to the 

 Pleistocene sea-level in about fifty thousand years ; and the 

 whole duration of maximum glaciation in Pleistocene times was 

 much longer than that. Moreover, in the case of many areas 

 this Pleistocene denudation was only the " finishing touch " to 

 subaerial denudation, which might have been continuously 

 going on previously. Some of the volcanoes, indeed, may 

 have been not merely pre-Tertiary, but even pre-Cambrian. 



Amelioration of climate followed, allowing coral life in the 

 waters where shallow platforms were now prepared for them. 



At the same time deglaciation caused a gradual deepening 

 of the sea. The coral growth would easily be fast enough to 

 keep the living zone of coral within twenty fathoms of the sur- 

 face during this deepening. The mechanism of growth, with the 

 resulting development of atoll, barrier and fringing reef forms 

 would be analogous to that imagined by Dai win on the 

 subsidence hypothesis. 



The theory of a general lowering of sea-level in inter-tropical 

 seas — counteracted in higher latitudes by the glacial attraction 

 — in no sense excludes complications due to local warpings of 

 the earth's crust. Other processes invoked by previous 

 writers have been so far neglected in the argument because 

 of the high probability that neither basin-foundering, nor 

 sedimentation, nor absorption of water by weathering rocks 

 seem to have been important enough since Tertiary times to 

 affect, by more than a fathom or two, the changes of level 

 assumed. 



METEOROLOGY. 



By JOH\ A. Cl'RTls. F.R.Met.Soc. 



The week ended November 19th, opened with extremely 

 unsettled weather in all districts, with heavy rain, snow and 

 sleet. Thunderstorms and hail were reported on several days. 

 In the South, however, there was a decided improvement in 

 the second half of the week. Temperature was below the 

 average everywhere, by as much as 7° in places, while 

 sunsliine was. on the whole, in excess. In Ireland and in 

 Scotland W,, the amount of rainfall for the week was below 

 the average, though the number of rainy days were in excess 

 there as elsewhere. The mean temperature of the sea water 

 was higher than that of the air on all our coasts, the excess at 

 Plymouth being 10°. The highest temperature reported was 

 5S° at Geldeston on the 15th, the lowest 18° at Marlborough 

 on the 1 7th. 



The week ended November 25th, was cold generally, but 

 the weather was finer in the Southern and Eastern districts 

 than in the Northern and Western. The defect in temperature 

 exceeded 9° at several stations, and at Prestwich it reached 

 10 . -At three stations in Ireland there was a slight excess. 

 The highest temperature reported for the week, 59°, was in 

 Ireland on the 23rd. The lowest minimum was 10° at 

 Balmoral on the same day. In Westminster the highest 

 reading was 43°, and the lowest 25''. The amount of rainfall 

 varied much. !n the English Channel it was three times the 

 average, and in Ireland S. nearly twice as much, while in 

 Scotland N, it was not quite half as much as usual. In the 

 tlastern districts generally the rainfall was in defect, and at 

 Spurn Head the week was rainless. Sunshine was in excess 

 except in the Southern districts. Balruddery reported the 

 highest aggregate, 22'7 hoars or 43 %. The mean temperature 

 of the sea water ranged from 53°'0 at Teelin to 40°'0 at 

 Pennan Bay. 



The week ended December 3rd, was, as a rule, dull and 

 unsettled, with frequent and long-continued rains. In the 

 extreme North, however, and in Ireland, the weather was 

 bright and cold. Aurora was seen in Scotland on November 

 29th and 30th. Temperature was low everywhere, the defect 

 exceeding 7 in places ; the highest reported reading was 56° 

 at Jersey on the 27th, the lowest 19°, at West Linton and 

 Markree Castle on the 30th. Rainfall again varied greatly, it 

 being only one-fifth of the a\erage in Scotland N.. while in 

 the Midland Counties it was five times the average. Falls of 

 1-in. and upwards in twenty-four hours were frequent, and at 

 Raunds in the four days, December 1-4, the total precipi- 

 tation was 4"23-ins. .Sunshine was in excess of the average in 

 Scotland N., and in Ireland N., but in no other district. At 

 Jersey the total duration for the week was only 5'8 hours 

 (10 %), while at Castlebay it was 33'4 hours (67 %). In London 

 the week was sunless. The mean temperature of the sea 

 water was greater than that of the air on all our coasts. The 

 individual readings varied from 53° at Plymouth, to 40° at 

 Cromarty. 



The week ended December 10th, was dull. niiUl and wet. 

 with a good deal of strong wind. Temperature was high 

 everywhere, the excess exceeding 6 at several places. The 

 highest readings reported were 57 ' at Cirencester on the 7th, 

 and at Llandudno on the 9th, the lowest, 29°, at Balmoral and 

 at Arlington. Over a large part of the kingdom the tempera- 

 ture of the air did not fall below the freezing-point, and on 

 the ground the minimum was only 25°, at Balmoral. The 

 rainy days were in excess of the average, and at many stations 

 rain was measured each day. The amount of rainfall was, 

 however, not excessive, except in England S.W., where it was 

 nearly twice as much as usual. In some districts, indeed, the 

 rainfall amount was in defect, and in Scotland N. it was but 

 little more than one-third of the average. Sunshine was 

 scanty in all districts. At Westminster the total duration was 

 only \'i hours (2 %) while the highest amount reported was 

 only 13'5 hours (25 %) at Felixstowe. The temperature of the 

 sea water \aried from 52 at Plymouth to 3'1 at Cromarty. 



