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FOR GENERAL READERS. 



Vol. I. — No. 21. (New Series.) 



FRIDAY, MAY asth, iJ 



rweekly, Price 30. 

 I By Post. Sjd. 



Scientific Table Talk 



Domestic Electric Lighting (illus.) ... 

 New Photographic Map of the Pleiades 



(j7/ttj.) 



Mulberry Trees 



Disinfection 



General Notes ... 



Simple Meteorological Instruments 



(?//«j.) 



Water-spouts and Whirlwinds (illus.) 

 Natural History : 



Poisonous Fishes. — II. The Sting 

 Ray (illus.), and the No'u 



Mother-of-Pearl in the Red Sea... 



Miscellaneous Notes 



PAGE 

 481 

 482 



485 



4S7 



490 

 492 

 493 



C ONTENTS . 



PAGE 



The Serpent-Mound of Ohio 493 



Thoughts on Instinct. — I. ... ... 494 



Reviews ; 



Precautions in Introducing the 



Electric Light 495 



Catalogo de los Cole6pteros de 



Chile 495 



A Manual of North American 

 Birds ... ... ... ... 496 



Journal of the Society of Tele- 

 graph Engineers and Electricians 496 

 Abstracts of Papers, Lectures, etc. : 



Royal Institution ... ... ... 497 



Iron and Steel Institute ... ... 497 



Society of Engineers 498 



Edinburgh Architectural Associa- 

 tion 499 



The Counting of Dust Particles in the 



Air 499 



Correspondence : 



Will Man Ever Fly— Lantern Fly 

 — Sir H. Roscoe's Report on the 



Treatment of Sewage 500 



Recent Inventions ... ... ... 5°' 



Technical Education Notes 502 



Announcements ... ... ... 503 



Diary for Next Week 503 



Sales and Exchanges ... ... ... 5°+ 



Selected Books 504 



Meteorological Returns 504 



SCIENTIFIC TABLE TALK. 



By W. Mattieu Williams, F.R.A.S., F.CS. 

 On page 43S of this magazine is an account of some 

 of the boulders found in coal seams, and a statement of 

 the ineifectual struggles that have been made to reconcile 

 their existence with the commonly-received notions of 

 the origin of coal. The writer concludes with the wise 

 suggestion that these boulders in coal seams require 

 much further study. 



Besides such study of the boulders, I think it very 

 desirable that we should further study the theory which 

 cannot, for the reasons stated by the writer, be reconciled 

 with what we already know concerning the boulders, 

 viz., " the doctrine that beds of coal have for the most part 

 been formed of the remains of trees and plants that grew 

 on the spot where the coal now exists ; the land having 

 been successively submerged, so that a covering of mud 

 and sand was deposited upon accumulations of vegetable 

 matter." (Lyell, " Principles of Geology," chap, vi.) 



Besides the boulder difficulty there are others equally 

 serious, such as the shells, and the bones, spines, and teeth 

 of fish found in coal, and another even more so. I refer to 

 the quantity and composition of the mineral matter, the 

 incombustible ash, of ordinary coal. To form a seam of 

 coal even three ieet thick in the manner supposed, 

 generation after generation of trees must have grown 

 and have left their trunks and leaves to accumulate. The 

 thickness of this loose deposit must have been many 

 times greater than that of the condensed coal ; some have 

 estimated it at ten times the thickness, but if only half ol 

 this the vegetable accumulation required to form the ten- 

 yard seam of South Staffordshire must have been 150 

 feet deep. We know that such trees cannot grow upon 

 the mere hydro-carbon of the dead bodies of their 

 ancestors ; there must be soil for the roots of each genera- 

 tion, and this soil must be largely composed of mineral 

 matter. Therefore, if the coal were simply the material 

 of the successive generations of forest trees, it must 

 include the mineral matter of the successive soils, over 

 and above that contained in the trees themselves. 



Instead of this being the case, ordinary coal contains 

 less mineral matter than exists in any of the plants 



which most nearly represent the vegetation of the coal 

 measures. The largest proportion of this mineral matter 

 is in the leaves which, being periodically shed, must have 

 constituted more of the vegetable deposit than the trunks. 

 Moreover, the composition of the mineral matter of the 

 coal is quite different from that of vegetables, which 

 select special constituents from the soil, and incorporate 

 them with their substance, but instead of such selected 

 material, the coal contains only theconstituents of the rocks 

 of the period, in rock proportions, not in vegetable ash 

 proportions. (See " Chemical and Physical Geology " by 

 Gustav Bischof.) The total quantity of mineral matter 

 in our ordinary bituminous coal varies from ^ to 2g per 

 cent, on the total dry material. 



If the coal were formed on the spot in the manner 

 supposed, the proportion of vegetable ash would be 

 greatly exaggerated by the fact, that as each year's leaves 

 are shed, their carbon and hydrogen oxidises, and leaves 

 behind a deposit of the special mineral matter assimi- 

 lated by the leaves, mixed with some humus. The pro- 

 portion of ash that would thus accumulate may be 

 demonstrated by burning a given weight of dried leaf 

 mould, and comparing its ash with that of the same 

 weight of coal completely burned. 



The raft theory suggested by Lyell is open to the 

 same or even greater difficulties ; the actual rafts of the 

 great rivers which suggested the theory contain far more 

 mineral matter than coal, and much of it in very gross 

 form — sand and pebbles. 



All these difficulties are met by the theory I proposed 

 some years ago — a theory founded on observation of 

 deposits now in actual progress, and now actually form- 

 ing coal seams on a scale of considerable magnitude. 

 The first of these observations was made in 1S55 at the 

 Aachensee, one of the lakes of North Tyrol, situated 

 about thirty miles N.E. of Innspruck. 



Its basin is the bottom of a steep valley, the slopes of 

 which are covered with a luxuriant forest vegetation. 

 The water of the lake is singularly clear, so clear that 

 the bottom is visible at great depths, and a curious sight 

 is there revealed. The bottpm is covered with thou- 

 sands of tree trunks most of them lying prostrate, but 



