ISS 



KNOWLEDGE. 



May. 1911. 



mass appears more promising. On the other hand, the forma- 

 tion of air passages, which is frequently advocated as a 

 remedy, seems likely to do as much harm as good, since the 

 heat of the oxidation promoted by the access of fresh oxygen 

 may more than counter-balance the heat carried away by 

 the air currents. 



THE BL.\CK GLAZING ON GRECIAN POTTERY. 

 — Many of the specimens of early Greek and Italian pottery 

 have been coated with a fine black glazing upon a terra cotta 

 ground, but the means employed to obtain this has long been 

 a lost secret. According to M. A. Verneuil, who has recently 

 published the results of his experiments upon the subject 

 iConipffs Rcndtis. 1911. CLII. 380), the pottery has 

 apparently been fired in an oxidising furnace : but the only 

 way in which he was able to produce a similar black enamel, 

 was by heating a flux containing magnetic oxide of iron in a 

 reducing furnace. A mixture of iron filings, sodium carbonate 

 and the powdered calcareous clay of the pottery itself yielded 

 a flux, which when heated in an oxidising furnace produced a 

 black glaze, which resembled the ancient black lustre in 

 showing a greenish sheen in reflected light, but was not equal 

 to it in depth of tone. 



INFLrEXCH OF CIlKdMUM COMPOUNDS ON 

 PL.4NTS. — .-Xn account of the experiments of Dr. P. Koenig, 

 upon the influence of certain chromium salts upon plant life is 

 given in the Clieiii. Zcntralblatt (1911. I, 498). From these 

 it appears that when applied in very small quantities chromium 

 compounds, and especially ehronious acetate, have a stimulat- 

 ing influence upon the germination and growth of plants, but 

 that in large quantities their action is very toxic, and has a 

 particularly injurious effect upon the roots. Solutions of 

 chromates are the most poisonous, but their action may be 

 minimised by adding an equivalent amount of lime to the 

 liquid, or by the addition of salts of metals, such as silver or 

 lead, which form insoluble chromates. In the case of plants, 

 such as lupins, however, to which lime is injurious, the 

 presence of the chromium intensifies the effect of the lime. 



The degree of toxic action also varies with the composition 

 of the plant, and the nature of the soil. Thus plants which 

 contain much silica oft'er the greatest resistance to the action 

 of chromates. while vegetation in a sandy soil is much more 

 affected than that growing in loam, probably on account of the 

 greater proportion in the latter of substances capable of 

 combining with the chromate. 



The amount of chromium taken up by the plant differs in 

 the case of different compounds, and it is remarkable that 

 alkali bichromates, which are the most toxic of the chromates, 

 give up least chromium to plants. There is also a greater 

 accumulation of chromium in the roots than in the other parts 

 of the plant. 



As the results of these experiments would indicate, a 

 solution of potassium bichromate has proved very effective as 

 a weed killer. 



C'.HoLouV. 



By Russell V. GwiwEr.L, B.Sc, .V.R.C.S., F.G.S. 



CLIMATE AND PHYSICAL CONDITIONS IN PRE- 

 CAMBRIAN TIMES. — In the January — February number 

 of the Journal of Geology, the oldest known rocks in 

 Canada .are dealt with by A. P. Coleman. Constituting 

 the Keewatin Series in the west and the Grenville and 

 Hastings Series in the east these pre-Huronian rocks 

 stretch for one thousand miles across the country. The 

 Huronian or Algonkian rocks, both sedimentary and 

 eruptive, are already admitted to have been formed like rocks 

 of later times. We find evidence in these early times of 

 climates not unlike those of later ages, when wind and 

 weather, flowing rivers, and beating waves and even great ice 

 sheets did their regular work. In northern Ontario glaciers 



formed boulder-clay in latitude 46" showing no hint of the 

 action of primeval heat such as the usually accepted \ersion 

 of the Nebular Hypothesis demands. 



But there is much less certaint\' regarding pre-Huronian 

 times. The world was already very old before the Huronian 

 ice-sheets began their work. Many geologists have been 

 inclined to see in the underlying " basal complex " portions of 

 the earth's original crust, of plutonic rocks and crystalline 

 schists consolidated from the cooling globe, which was still 

 too hot to permit the condensation of water, so that no rivers 

 or oceans were possible. The conviction, however, is growing 

 in the minds of many geologists that, although the Huronian 

 basal conglomerate means a break in time, it does not mean 

 a break in the continuity of marine and terrestrial processes, 

 but that the affairs of the world were conducted in the same 

 way before this great inter\al as after it. 



The author then shows that these pre-Huronian rocks 

 include large amounts of sedimentary materials — limestones, 

 dolomites, slates, gneisses having the composition of clayey 

 sandstones, and so on. In the east the seas were clearer and 

 deeper and limestones predominated, while in the west volcanic 

 activity was very pronounced producing thousands of feet of 

 ashes. and so on. There must have been great land-surfaces from 

 which rivers flowed bringing down sand and clay. The sea 

 contained plants to furnish the carbon (often reaching several 

 per cent, in slates, gneisses and limestones! while the lime- 

 stones hint at calcareous algae or animals having hard parts. 



Similar sediments penetrated by granites and gneisses 

 occur in the Lewisian of Scotland and in the Ladogian of 

 Finland, and so on. 



It is thus evident that the Keewatin and Grenville Series 

 of .America, like the oldest rocks of Europe, do not take us 

 back to the commencement of geological time, since they 

 include clastic sediments which imply the weathering and 

 erosion nf previous rocks before they were spread out on the 

 sea bottom. "We have extended our outlook much farther 

 into the past, but there is still an impenetrable background 

 beyond. V\'e shall perhaps never be able to say ' m the 

 beginning ' ; but we may safely say that there is no hint of a 

 molten earth in process of cooling down. If the earth was 

 ever hot it had so far cooled down before the oldest known 

 rocks were formed as to allow air and water and life to do 

 their work in the world very much as they do now. If the 

 earth ever passed through a period of great heat it was at 

 a time too remote in the past to leave a geological record or to 

 have any special interest for the geologist." 



THE GEOLOGISTS' ASSOCIATION.— The Geologists' 

 .Association celebrated the fiftieth anniversary of its founda- 

 tion by the publication of a useful work entitled " Geology in 

 the Field : the Jubilee Volume of the Geologists' .Association." 

 This book, edited by Messrs. Monckton and Herries, has 

 within the last few months been completed by the issue of 

 Part \'. 



The places visited during the fifty years' existence of the 

 Association were arranged in groups or districts, and a number 

 of geologists, selected for their special knowledge of the 

 localities, were asked to contribute descriptive articles on the 

 respective districts, using the previously issued reports of the 

 excursions as a basis. The scope of the work is confined, 

 however, to England and Wales. 



Hardly is this book completed before the work of the 

 Geologists' Association comes once more before the general 

 public. For, on behalf of the Association, Dr. J. W. Evans 

 is arranging a series of exhibits in the Science Section of the 

 Coronation Exhibition at Shepherd's Bush. These exhibits, 

 intended to illustrate the work of the Geologists' Association, 

 consist of maps and relief-models of districts visited and 

 geological specimens collected by members from these districts. 

 By the time these notes are published, the exhibition will 

 probably be open, 



A NEW INDUSTRY IN THE HEBRIDES,— The finding 

 of iron ore in Raasay, one of the islands of the Inner Hebrides 



