272 



KNO\VLi:nGE. 



Ifl.Y, 191: 



In Cdiincction with these iiivcsliMations it was discovcrcJ 

 that the light rays emitted by sails of radium could be 

 transmitted throufih (|uart/ plates of a certain thickness, 

 while the a, ,i and 7 rays were absorbed. 



GEOLOGY. 



By G. W. Tyrrell, A.K.C.Sc, F.G.S. 



THE MINI:K.-\LS of TONOFAH. NEVADA.— a paper 

 with this title is issued as Number 1 of the seventh volume of 

 the Hullelin of the Department of (ieoloKy, University of 

 California, and is written by A. S. Eakle. The Tonopah 

 minerals occur in the great silver deposits of that district, and 

 were previously mentioned by Spurr in his monograph on the 

 Tonopah mining district. The typical ore consists of agangue 

 of massive white quartz and felspar, with blotches and bands 

 of granular, black, silver minerals, pyrites, chalcopyrite, galena, 

 blende, and occasionally flakes of free gold. It is deposited 

 in an igneous rock, first designated by Spurr as " earlier 

 andesite," but now recognised as trachyte. The Tonopah ore 

 occurs in an arid region, in which simple hydration is not the 

 dominant mode of weathering. What surface waters there 

 are work downwards over the veins, strongly charged with 

 soluble material from the overlying and adjacent rocks, and 

 complex oxidations with unusual mineral precipitations result. 

 The most important minerals in the zone of oxidation are the 

 three silver haloids, cerargyrite, embolitc and iodyrite, but 

 numerous other rare minerals are obtained. 



THE VOLCANOES OF MADAGASCAR.— Professor A. 

 Lacroix, now the only one remaining of the brilliant trio of 

 French petrologists, the other two members of which were 

 Michel-Levy and Fouque, writes on the volcanoes of the 

 French colonies in the Indian Ocean, especially those of 

 Madagascar, in an address to the Congres des Societes 

 Savantes k Paris (April, 1912). Madagascar contains many 

 volcanoes, both ancient and comparatively recent. The island 

 is built up of a mountainous backbone consisting of crystalline 

 schists and granite, rising abruptly out of a sandy plain on the 

 east coast, and from under extensive stratified formations on 

 the west. 



Volcanic rocks abound in the midst of the sedimentary 

 series. The principal centre is at Ankaratra near the centre 

 of the island. The lavas of Ankaratra can be followed with- 

 out interruption for over one hundred kilometres from North 

 to South, and fifty kilometres from East to West. The total 

 area covered by the volcanic rocks is certainly not less than 

 four thousand square kilometres. It is believed that these 

 belong to the Tertiary period, but in the absence of intercalated 

 sediments and fossils it is impossible to date them exactly. 

 Scoria cones and craters, still intact, show that the volcanic 

 activity persisted until a very late period. 



Vulcanism began in the Ankaratra massif by a deluge of 

 black lavas — felspathic basalts — which, to judge by the extent 

 of their flows, must have been emitted in a state of great 

 liquidity. These lavas were erupted from a long series of 

 volcanoes aligned in a N.N.E.-S.S.W. direction. After this 

 outburst, the centres of activity became more localised and 

 differentiated. In the centre and south of the massif, mica- 

 trachytes were erupted, and in the south-west, alkali-trachytes 

 and phonolites. After this extravasation of pale-coloured 

 rocks a series of black nephelinites were erupted, descending 

 in all directions from the high summits of the chain. The 

 phonolilic rocks of the south-west arc remarkable for the fine 

 dome-topography they present. The same topography is 

 found in a second, but smaller, massif, that of Itasy, to the 

 north-east of Ankaratra. The phonolite domes or puys are 

 here accompanied by very recent cones of basaltic scoria, and 

 rest upon an undulating surface of ancient rocks, thus reproduc- 

 ing the essential features of the chain of puys in Auvergne. 

 " Imagine," says Professor Lacroix, "the latter transported to 

 the side of one of the Italian lakes, with its blue waters and 

 azure sky, and you will have some idea of the marvellous 

 panorama furnished by the Itasy region. If, however, the 

 local colour is to he preserved, it would be necessary to people 

 the lake with enormous crocodiles ! " 



Mi:ri':()R()LOGV. 



By John A. Curtis, F.R.Met.Soc. 



The weather of the week ended May 18th, as set out in the 

 Weekly Weather Report issued by the Meteorological Office, 

 was changeable. Rain was reported in all districts, thimder- 

 storms were experienced on four days, and a sharp line squall 

 passed over the Midlands on the 16th. 



Temperature was above the average in all districts except 

 Scotland, N. and W., and in Ireland. The highest readings 

 were 74° in Jersey on the 12th. 73° at Tottenham and 

 Camden Square on the 14th, and 72° at Greenwich and 

 Southampton on the 12th. The lowest of the minima were 

 27° at Balmoral on the 13th, and 30° atColmonell and Newton 

 Rigg. Temperatures at or below the freezing point were 

 reported from six districts. In the English Channel the 

 lowest reading was 45°. On the ground the temperature fell 

 to 23° at Balmoral and Newton Rigg and to 24° at Crathes. 

 The soil temperature both at one foot and at four feet depths 

 remained above the average of past years. 



Rainfall was in excess in Scotland, N and E., and in England 

 N.E., S.E. and the Midland Counties, but was in defect else- 

 where. At a few places in Scotland and at Buxton the total 

 precipitation for the week exceeded one inch, and at Wick it 

 exceeded two inches, but generally the amounts were light. 

 At Holyhead no rain was measured. Sunshine was above the 

 average in most districts, markedly so in Scotland. E. and W., 

 and in England, N.W. The sunniest district was Scotland, W. 

 with a daily average of 9-4 hours (59%). The least sunny 

 districts were the Midland Counties and England S.W., with an 

 average of 5-9 hours a day (3cS°o). The sunniest station was 

 Douglas, Isle of Man, where the amounts registered equalled 

 a daily average of 11-5 hours or 72 per cent, of its possible 

 duration. 



The mean temperature of the sea water round the coasts 

 varied from 46° -0 at Berwick to 55' -9 at Eastbourne. 



The weather of the week ended May 25th was generally 

 cool, cloudy and unsettled. About the middle of the week 

 thunderstorms were reported in the midland and eastern 

 counties. 



The mean temperature was above the average in England, E. 

 and the English Channel, but below it elsewhere. The 

 greatest deficiency was in Scotland. E., where the average 

 value was only 46° -3 as compared with the average over 

 twenty-five years of 49°- 6. The maxima were low. In only 

 four cases were temperatures of 70° or upwards reported, 

 namely 72° at Greenwich, and 71° at Camden Square and in 

 Jersey and 70° at Raunds. In most cases these occurred on 

 the 19th. At all other stations the maximum for the week 

 was less than 70°, and in Scotland. W., and England, N.W.. 

 the highest readings did not exceed 64°. The lowest readings 

 for the week were 28° at Balmoral and 29° at West Linton 

 and Markree Castle. In the English Channel the mininnun 

 did not fall below 46°. On the grass low readings were again 

 reported, down to 22° at West Linton, and 24° at Crathes 

 and Newton Rigg. 



The temperatlue of the ground at one foot depth was 

 generally below the average but at four feet depth it was still 

 in excess. Rainfall varied greatly. In England. N.E. and the 

 Midland Counties it was very heavy, at some stations four 

 times as much as usual. In Scotland, on the other hand, the 

 week was dry and in Scotland. N. the total was less than a 

 quarter of the average amount. At Spurn Head, which is 

 usually one of the stations with least rainfall, the total for this 

 week was 2-07 inches as compared with an average of 0-36 

 inches. 



Sunshine was in defect in all districts except Scotland, N., 

 ■and the English Channel. The last-n.inied district had the 

 largest daily average amount. 9- 6 hours (62%). but Scotland. N. 

 reported 8- 1 hours (48%), while the Midland Counties had only 

 4 • 2 hours (26%). The station reporting the greatest duration of 

 sunshine was Decrness, Orkney, 11-2 hours (65%). At 

 Westminster the average for the week was 4-9 hours (31%). 



The mean sea temperature ranged from 46° -8 at Berwick 

 to 56'^'6 at Margate. 



