Mav. 1912. 



KNOWLEDGE. 



189 



east and north-east of Mansfield, the Top Hard Coal may be 

 found at workable depths throughout most of the area 

 described in the memoir. 



COPPER NICKKL ORES I \ E.AST GRIgU.\L.\ND.— 

 .\ great nickel-bearing intrusion, very similar to that of the 

 l.imoiis Sudbury district of Canada, has beenfound.it Insizwa. 

 ICast Griqualand. and has been described by A. L. Du Toit in 

 The Fiftccntli Aiiiiiial Report of the Geological Coiiiniis- 

 sion of Cape Colony (19101. The intrusion consists mainly 

 of gabbro, with olivine- and hypersthenebearing varieties, 

 intruded into the shales and sandstones of the Beaufort Series, 

 which it has intensely metamorphosed. The chief ore 

 minerals arc pyrrhotite, chalcopyrite, and pentlandite. The 

 latter, of course, is the chief nickel-bearing mineral, but the 

 other two are also slightly nickeliferous. These ores are 

 confined more or less to the contact of the gabbro with the 

 hornfelsed sediments, impregnating the latter to a small 

 extent, but becoming more abundant in. and sometimes 

 restricted to. the igneous rock, of which the sulphide ores 

 appear to be primary constituents. 



.\s ill the Sudbury district, the Insizwa intrusion forms a 

 huge basin-shaped mass ; but the shape is original, and is not 

 due, as at Sudbury, to the sinking of the sediments in the 

 basin. The strata have been intensely altered, in some places 

 to a depth of two hundred feet below the intrusion. The 

 resulting hornfels is much mi.\ed np with the gabbro near the 

 contact, and is also penetrated by strings and patches of 

 granitic rock. The copper-nickel ores occur along the lower 

 contact of the gabbro, and ne\er more than a few feet away 

 from the igneous rock. 



The gabbro must be regarded as the source of the ore, for 

 a petrological examination of the ore-bodies shews that the 

 ores formed a portion of the once molten magma, and that 

 during the cooling they segregated towards the lower margin 

 of the mass, impregnating the adjacent strata to a small 

 extent. The order of crystallization of the chief ore minerals 

 is (1) Chalcopyrite. (21 Pentlandite, (3) Pyrrhotite. The 

 olivine and pyro.xenes in the igneous rock are beautifully 

 fresh, and are idiomorphic to the ores ; but the latter appear 

 to have crystallized along with the biotite. In places the ore 

 is moulded on the biotite. in others it is iutergrown to a small 

 degree, but commonly the biotite forms a fringe around the 

 ores. No veins of sulphide ore are to be found penetrating 

 the gabbro minerals as one would expect had water 

 deposition been the agent of their formation. 



There is every stage from a gabbro or norite with miimte 

 scattered particles of ore to a rock in which ore and silicates 

 are in equal proportions, and finally to an almost pure ore 

 with a few patches of silicates scattered through it. The pure 

 ore-bodies are usually sheet-like in form, and are roughly 

 parallel to the adjacent contact, grading into normal gabbro. 

 There is a gradual decrease of basicity in the mass from the 

 bottom to the top. Towards the top the rock becomes 

 olivine-fre(\ and a quartz-felspar micropcgniatite is developed. 



It is to be hoped that future mining developments will show 

 that the Insizwa Range is similar to the Sudbury district in 

 the richness of its ore-deposits, as well as in their form and 

 genesis. 



THE DATA OF GEOCHEMISTRY.— Dr. F. W. Clarke 

 and the United States Geological Survey deserve the thanks 

 of all geologists for the second edition of " The Data of 

 Geochemistry," issued recently as Bulletin 491. All that 

 relates to the chemistry of geology is here dealt with in 

 detail, and the geologist willbe no less thankful for the scope 

 of the work than for the extremely full references to the vast 

 and widely-scattered literature of the subject. Originally 

 issued in 190S as Bulletin 330, the book is now revised, 

 enlarged and brought thoroughly up-to-date. The petrologist 

 and mineralogist, as well as workers in other branches of the 

 science, will find in this book a perfect mine of facts relating 

 to the chemical side of their study. 



THE MESOZOIC ROCKS OF KENT.— The mesozoic 

 rocks obtained in four of the principal borings for coal in 

 Kent have been examined in great detail by Messrs. G. W. 



Lamplugh and F. L. Kitchin, of the Geological Survey, and 

 the results published in a recent Survey Memoir. \ know- 

 ledge of the range and character of the Mesozoic rocks in the 

 south-east of England is of much importance as bearing on 

 the prospects of finding coal at a workable depth in the 

 Palaeozoic lloor which underlies the area. Such investigations 

 lead to conclusions as to the thickness of rock to be penetrated 

 before the coal-bearing strata are reached, and may afford 

 indications as to the localities where borings may be under- 

 taken with the most profitable results. Four borings, at 

 Dover, Brabourne, Pluckley, and Penshurst, ranging on an 

 east-west line of forty-five miles, are described. 



Some very important results have been obtained, which have 

 no little bearing upon the economic problem. The Lower 

 Cretaceous rocks imderground vai-y considerably from their 

 outcrop characters. At Dover the palaeontological evidence 

 establishes an imconformity between the Hastings Beds and 

 the Kimmcridge Clay, only the lower part of the clay being 

 represented. To the west, however, the upper part of the 

 Kiuuneridge Clay is so greatly developed that the Penshurst 

 boring failed to penetrate to its base. This thickening is 

 shared by all the Jurassic and Lower Cretaceous strata, and 

 indicates a long-continued depression in this region. The 

 downward movement ceased before the deposition of the 

 Upper Cretaceous, and the Wealden anticline has since been 

 superimposed upon the whole area. Characters indicative of 

 a shore-line to the north-east have been observed in several 

 of the Jurassic rocks. 



METEOROLOGY. 



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



The weather of the week ended March 16th, as set out in the 

 Weekly Weather Report of the Meteorological Office, was 

 generally unsettled, although in some places no rain was 

 recorded. Thunder was heard in Hampshire on the 15th, 

 and sleet or snow was experienced in Ireland towards the 

 end of the week. 



Temperature was considerably above the average in all 

 districts, but only in Ireland, S. did the maximum reach 60°. 

 The highest readings were 63" at Foynes and Killarney on the 

 13th. with 62' at Kilkenny, and 61° at Cahir. In Jersey the 

 maximum was only 57°. The lowest readings were below 

 freezing-point in all districts except Ireland, N. and the 

 English Channel. The lowest of the minima were 21° at 

 Balmoral and 25'' at West Linton. On the grass the 

 temperature fell to 18° at Balmoral and to 19° at Newton 

 Rigg. but at depths of one foot and four feet the earth 

 temperature was higher than usual in all parts. 



Rainfall was below the average in Scotland, N. and E., and 

 just equal to it in England, E. and S.E. In all other districts 

 it was in excess, though not as a rule to any great extent. 

 Sunshine was slightly above the average in Scotland, N., and 

 Ireland, S., but below it elsewhere. The district values varied 

 from 1-6 hours per day (13%) in England, E., to 3-8 hours 

 per day (33%) in Ireland, S. At Westminster the average 

 duration was 1 -2 hours per day, or 10 per cent, of its possible 

 duration. 



The temperature of the sea water round the coasts varied 

 from 40° at Berwick and Scarborough to 51° at Scilly. 



The weather of the week ended March 23rd was very 

 unsettled. Over a large part of the Kingdom precipitation 

 occurred every day, generally in the form of rain but some- 

 times in that of sleet, snow or hail. 



Temperature was not far from the mean but was below the 

 average in most districts. Frost was experienced in all districts 

 except the English Channel. The lowest readings reported 

 were 23' at West Linton, and 26° at Fort Augustus. In Jersey 

 the minimum was 35°. The highest maximum was 60° at 

 Killarney, the next highest being 55° at Cambridge and 

 Cirencester. On the grass, readings down to 19' at Ranceby 

 and Newton Rigg and 20° at \\'orksop were reported, while the 

 temperature of the earth, both at one foot and at four feet 

 depths was from 2° to 5' higher than usual. 



Rainfall was above the average in all districts except Scot- 



