September 14, 1893] 



NA TURE 



459 



Geological Map of Cape Colony, 1873, published by Stanford, 

 London. 



In the southern portion of Cape Colony no formation has ex- 

 cited so much interest, or proved so inscrutable a puzzle to the 

 earlier geologists, as the zone of rock named " Porphyry 

 and "Trap Conglomerate" by the late A. E. Bain, 

 "Trappean Ash" by Wylie, " Metamorphic Rock" by Pin- 

 chin, &c., and called "Bushman Graves" by the Boers. In 

 Natal the same formation occurs, and Dr. Sutherland (of that 

 colony) was the first to consider it as possibly of glacial origin, 

 but he obtained no direct evidence to support that view. 



As the names applied to this singular conglomerate were all 

 misleading in my Sketch Geological Map of 1875, I named 

 it the "Dwyka Conglomerate," on account of the excellent and 

 characteristic sections exposed where the river of that name cuts 

 through it. 



While at Matjes Fontein, Cape Colony, in June, 1885, I 

 obtained the first evidences of glaciation in this southern exten- 

 sion of the conglomerate among the loose pebbles, and more 

 abundant evidence at Prince Albert, close by. In my report of 

 1886 to the Cape Government, the full extent of these con- 

 glomerates in South Africa is shown. Incidental reference and 

 sections of the conglomerate occur in my report to the Cape 

 Government dated 1879. The full extent of the conglomerate 

 is also shown in my Sketch Geological Map of South Africa 

 of 1887, published by Sands and McDougall, Melbourne. 



Australia. — In 1887 I obtained indubitable evidence of 

 glaciation in the conglomerate of Worragee, near Beechworth, 

 Victoria, and placed well-striated pebbles and boulders in the 

 local museum and in the Technological Museum, Melbourne. 

 These were the first glaciated stones discovered in the palaeozoic 

 conglomerates of Victoria. Shortly afterwards, on visiting 

 Bacchus Marsh and the Wild Duck Creek, I obtained abundant 

 and unchallengeable testimony to the glacial origin of these con- 

 glomerates also for the first time, although their glacial origin 

 was suspected thirty years ago by Sir A. Selwyn and the late 

 Mr. Daintree. A paper on the subject was read before the 

 Royal Society of Victoria in 1887, and several localities besides 

 the above described. Another was read before the Australasian 

 Association Meeting, December, 1890. A special report on 

 the Wild Duck Creek conglomerate, prepared in 189 1 for the 

 Geological Survey Department, was published in 1892. 



Tasmania. — In October, 1892, I once more encountered this 

 remarkable conglomerate at the base of Mount Reid, near 

 Strahan, and at an elevation of 3000 feet above sea-level. At 

 this site it corresponds in a remarkable manner with both the 

 Dwyka conglomerate of South Africa and the Wild Duck Creek 

 conglomerate of Victoria. At the same time, and at a few 

 miles' distance, I discovered around Lake Kora very extensive 

 and marvellously well developed evidences of modern glaciation 

 on a large scale. These discoveries were made public through 

 the press at Hobart and at Melbourne in the beginning of No- 

 vember following, and a paper and plan has been submitted to 

 the Royal Society of Melbourne, and read. The whole of my 

 reports and maps have been supplied to the Geological Society, 

 Burlington House. E. J. Dunn. 



Melbourne, July 15. 



Astronomical Photography. 



Lord Raylhigh, in his letter (August 24), raises the inter- 

 esting question of the adaptability of the plate to the object- 

 glass. This is a novel idea, and I hope with him that we shall 

 have the opinion of Captain Abney or some other authority on 

 the question, or that it will be settled experimentally whether 

 the use of an object-glass corrected for visual work will give, 

 with properly prepared plates, results approximating those 

 obtained with the photographic object-glass. In the case of 

 Cambridge Observatory, there is already an object-glass of 

 nearly twice the area of the proposed photographic telescope, 

 so that it is quite possible as good results might be obtained 

 with the Newall telescope as with the proposed one. 



With the collodion process, where the curve of sensibility of 

 the photographed spectrum had a well-defined summit, the 

 photographic object-glass corrected for that part left very little 

 to be desired. Now, the curves of sensibility of the different 

 kind of plates vary extremely. We have long flat curves, or 

 curves with two maxima ; in fact, there is such a range now that 

 it is a matter of surprise to me that any object-glass produces 

 such good results as are obtained. Some years ago, after read 



NO. 1246, VOL. 48] 



ing Dr. H. W. Vogel's "Photography of Coloured Objects," 

 I thought that astronomers would be driven to the use of the 

 only instrument that will use any and every plate— the 

 Reflector; or if they would use the object-glass, that they would 

 have to first find the most sensitive plate, and then make their 

 object-glass to suit it. They should be made to suit each other. 

 If this can be done by a variation of the photographic process 

 without paying too dearly for it in the loss of sensitiveness, a 

 great deal will be gained in many ways. 



The great doubt in my mind is whether it is possible to get 

 rid of the blue rays without the use of screens. 



In any case, the object-glass can never properly use all the 

 available light in the way the Reflector does, and it is a matter 

 of extreme surprise to me that, notwithstanding the magnificent 

 results obtained by the Reflector in astronomical photography 

 astronomers still seem to prefer the expensive object-glass. 



Ealing, September 11. A. A. Common. 



The Greatest Rainfall in Twenty-four hours. 



As a resident of Dehra Dun, I was interested in a paragraph 

 at p. 297 of Nature for July 27, 1893, saying that the Indian 

 Planters'' Gazette had recorded a rainfall of 48 inches at Dehra 

 Diin on the nighl of January 24, 1893. As 48 inches is con- 

 siderably more than half our average yearly rainfall (86 inches). 

 1 have looked up the official returns of the Meteorological Re- 

 porter to the Government of India. They give for the rainfall 

 recorded at 8 a.m. on January 24, 1893, o'26 inches only, 

 I '07 inch being the recorded fall on the same date at Mus- 

 soorie, on the hill range li miles off. I have examined the 

 Dehra Dun rainfall records since January I, 1867, and find that 

 the largest amount recorded for any one day since that date is 

 1 1 '60 inches, which is given for July 30, 1890. It is possible 

 that the correspondent referred to wrote 48 inches, but even 

 that amount, though not an uncommon fall for the monsoon 

 season between June and September inclusive, would be a 

 heavy fall for January. The highest recorded fall for any day in 

 January is 2 84 inches on January 26, 1883. 



J. S. Gamble. 



Imperial Forest School, Dehra Dun, Aug. 22. 



[The paragraph in question was taken from Ihe Ceylon 

 Observer. We append it as it appeared in our issue for July 27, 

 together with a remark we made ; t the time. — Ed.] 



" If the Indian Planters' Gazette of 28 Jan., 1893, is correct, 

 the following paragraph establishes a still higher record. On 

 page 59 one reads : ' Our Dera Doon correspondent writes on 

 January 24, 1893 : last night we had 48 inches of rain, and all 

 the hills are covered with snow. It is still raining.'" For 

 this to have any scientific value, however, it must be known 

 who were the observers, and by what means the rainfall was 

 gauged. 



Wasps. 



Of late much has been written about the seasonal prevalence 

 of wasps, and the mischief, in several places, wrought by them. 

 May not, however, their use in keeping down many forms of 

 insect pests be set off as some sort of palliative ? Wasps are 

 exterminators of aphides, and although the season has been 

 favourable to insect-life, next to no damage has been done to 

 the hopbines or the corn or pulse crops of Worcestershire or 

 Herefordshire by these latter pests — frequent destroyers of 

 crops. 



Is it suggestible that the excessive wasp prevalence is attri- 

 butable in some measure to the abundance of their insect prey, 

 just as has recently happened in Scotland, in the instance of 

 the multiplication of the short-eared or " Woodcock " owl, 

 owing to the plague of field voles? The owl is a winter immi- 

 grant, usually leaving in spring. "Nests in ordinary seasons 

 are of rare occurrence in Great Britain, but owing to the vast 

 increase of their favourite food — the field vole — -these owls 

 have not only arrived in increased numbers, but have remained 

 and bred in Scotland all over the affected districts, laying from 

 eight to thirteen eggs, and rearing large broods," instead of 

 the few eggs these owls have hitherto been accredited with 

 laying. 



I am a fruit grower. Much damage has this year been done 

 to the fruit ; not, however, by the wasp tribe, but by hungry 

 birds, the fruit having even been attacked in an unripe state. 

 According to my experience wasps do not become household 

 pests till the falling-off of insect prey towards autumn. 



Worcester, September i. J. Lloyd Bozward. 



