December, 1913. 



KNOWLEDGE. 



465 



reduced to a mere trickle. Under microscopic examination 

 the crystals were found to be colourless, of rhombohedral 

 habit, and giving the usual tests for calcite. This determina- 

 tion was confirmed by chemical analysis, which showed that 

 the deposit contained 95 • 65 per cent, of calcium carbonate, the 

 rest being alumina, ferric oxide, and silica. The deposition 

 of these crystals under artificial conditions of comparative 

 aridity has a bearing on the formation of similar carbonate 

 crystals in ancient sediments laid down under arid conditions, 

 under which direct precipitation of carbonates from solution 

 may well have taken place. 



LAND CLASSIFICATION AND GEOLOGY.— Recently 

 the people of the United States became aware that they had 

 been too lavish with their lands, and that more than half the 

 public domain had been alienated. Now, therefore, the 

 examination and classification of the public lands has been 

 made an essential preliminary to their disposition and develop- 

 ment, and the Geological Survey was commissioned to carry 

 out a scientific examination of the lands still remaining to the 

 nation. Pending the accumulation of this quantitative 

 knowledge the land is withdrawn from settlement and 

 exploitation ; but as soon as any area is accurately known, and 

 its highest use ascertained, it is restored to entry, and is so 

 disposed as to secure the maximum benefit to both settler and 

 State. From the results of geological examination by its field 

 officers the Land Classification Board of the United States 

 Geological Survey is enabled to say whether the highest 

 utilisation of certain areas may be attained by working 

 metalliferous deposits, coal, oil, gas, phosphate, or salines, or 

 by using it as a reservoir or water-power site, or merely as 

 agricultural land. On the basis of information thus obtained 

 the public-land administrative officers make the most useful 

 allocation of the land that is possible. In the case of coal a 

 most exact quantitative survey is made, and a valuation 

 becomes possible. After classification and valuation the 

 lands are restored to entry, and may be acquired under the 

 coal-land laws at the valuation prices. Prior to land- 

 classification many persons fraudulently obtained coal and 

 other valuable mineral lands under the cheap and easy mode 

 of entry relating to agricultural lands. The principles, 

 purposes, and methods of land classification are explained in 

 Bulletin 537 of the United States Geological Survey, which 

 makes most interesting reading. It presents a clear formula- 

 tion of a new method in which the science of geology is made 

 of practical value to the public. Although it is rather late in 

 the day to voice the sentiment it is perhaps a pity that all the 

 public land of our own country is so hopelessly alienated. 



ORIGIN OF TEKTITES.— Under the term "tektite," 

 Professor Suess includes all the peculiar pebbles of obsidian- 

 like glass which have been described under the names of 

 moldavite, billitonite, and australite. These have frequently 

 been assigned an extra-terrestrial origin ; and Dunn regards 

 australites as the blebs from the bases of glass-bubbles ejected 

 from volcanoes and distributed by the wind over the Australian 

 plains (see " Knowledge," August, 1913, page 308). G. P. 

 Merrill hasrecently compared tektites with a series of undoubted 

 obsidian pebbles from various localities in North and South 

 America and Iceland, and finds that the latter have the same 

 structures and peculiarities of surface-markings as the tektites. 

 Moreover, he shows that the chemical composition of one of 

 these obsidian pebbles does not sensibly differ from that of 

 tektites (Proceedings U. S. Nat. Mus., 1911, 481-6). Dr. 

 Merrill concludes that while the theory of the meteoric origin 

 of tektites is not controverted by these observations, it cannot 

 be regarded as proved until these bodies have actually been 

 seen to fall on to the earth's surface. 



In connection with Dunn's theory of the origin of australites, 

 the observation by Mr. F. W. Moon of volcanic ash in Mexico, 

 consisting largely of perfect bubbles of volcanic glass, is of 

 great interest and importance (see letter in " Knowledge," 

 November, 1913, page 409). It proves what Dunn was unable 

 to prove, that volcanic glass-bubbles are capable of being 

 formed and of being distributed over the earth. More inform- 

 ation concerning this occurrence is desirable. 



METEOROLOGY. 



By William Marriott, F.R.Met.Soc. 



DURATION OF RAINFALL.— It is generally believed 

 in this country that every other day is a wet one. This 

 supposition is approximately correct, as the number of rain 

 days " in the year is about the same as the number of rainless 

 days. A " rain day " is held by meteorologists to be a day 

 on which an amount of 0-01 inch or more fell during the 

 twenty-four hours ending 9 a.m. of the next day. This may 

 be spread over the whole twenty-four hours, or it may only 

 occupy a few minutes in falling, but it gives no information as 

 to the actual duration of the rainfall. This can only be 

 obtained from self-recording rain-gauges, and it is satisfactory 

 to learn from British Rainfall that there is an increase in 

 the number of these instruments in use. 



At Camden Square, London, where a Casella self-recording 

 rain-gauge has been in use since 1881, the following are the 

 average values for the thirty-one years, 1881-1911 : — 



Rainfall. Duration. Intensity Rain days. 



rate per hour. 



24-13-in. 426-9 hours. -057-in. 162 



In 1912 the values were : — 



Rainfall. Duration. Intensity Rain days. 



rate per hour. 

 27-88-in. 516-2 hours. -054-in. 180 



The duration in 1912 exceeded the average by twenty-one 

 per cent., and the number of rain days eleven per cent, in 

 excess of the average for the same period ; the year was thus 

 one of very persistent rainfall, but with an intensity slightly 

 below the normal. 



The following values from the same class of instrument 

 show the monthly duration of rainfall in hours at several 

 stations in various parts of the country during 1912 : — 



April stands out prominently as a very dry month, the 

 duration of rainfall in many districts being less than two 

 hours. The months of greatest duration were January, 

 March, and August. It is interesting to notice that in the 

 mountainous districts, where there is a heavy rainfall, the 

 duration is considerably greater than at stations at a much 

 lower elevation. 



TORNADO IN WALES.— We are accustomed to think 

 that tornados only occur in the United States and that nothing 

 of the kind is likely to be experienced in the British Isles. 

 On Monday, October 27th, however, a little after 5 p.m., a 

 most violent storm of the tornado type, accompanied by vivid 

 lightning and heavy rain, occurred in South Wales and passed 

 over the district in which Senghenydd is situated, where the 

 recent appalling colliery disaster occurred. From the 

 accounts in the local papers it appears that the storm started 

 on the mountain west of Treforest and rushed up the 



