268 



KNOWLEDGE. 



July, 1913. 



America were driven farther east till the last bond with the 

 great eastern land-mass failed, and the ocean lapped the 

 bounds of Mauretania. 



GREAT EXPLORERS. — The geographical journals have 

 recently been full of appreciations of Livingstone, and the 

 fact has emerged that it is at least largely as a geographer 

 that he will be remembered. To him is due a revolution in 

 African exploration, and to his influence can be traced a 

 beneficial effect on exploration generally. His mistakes, and 

 particularly his curious tenacity in entertaining certain pre- 

 conceptions in the face of contradictory facts gathered in his 

 own work, have been made much of by certain critics. The 

 wonder is that the accuracy of his observations and results 

 has never been impaired under the influence of his prejudices. 

 His maps show accuracy proportional rather to his energy in 

 utilising stray opportunities of gaining instruction than to the 

 extent of his training. It is related of him that he spent his 

 time on his first voyage largely in learning from the captain of 

 the ship how to determine positions by means of the sextant 

 and in mastering the art. The result is that some of the 

 stations he fixed were determined with sufficient accuracy even 

 for many modern requirements. No man has made greater and 

 more valuable changes on any map than he on the accepted 

 map of Africa: to realise this one has but to glance at the 

 series of maps earlier and later than his, published recently in 

 the magazines. By virtue of his inborn capacity for leader- 

 ship and the management of men, and his sympathetic 

 grasp, he was able not only to bring away stores of informa- 

 tion regarding the topographical and racial geography of 

 Africa, but to leave behind the influence of a master mind 

 and heart. 



The Geographical Journal for June publishes an account, 

 by Sir Clements Markham, of Vasco Nunez de Balboa, that 

 singular man who reached Darien, " headed up in a cask," a 

 fugitive on the ship of Enciso. At the helpless fort of 

 Darien, in the midst of Indians, whose distrust and enmity 

 had been aroused by Spanish cruelty and injustice, he was 

 recognised as a born leader, and was obeyed by Pizarro 

 himself, who was actually in charge. He regained the con- 

 fidence of the natives, though with difficulty, and contrived to 

 render the existence of the hitherto wretched fort possible. 

 Informed by natives of the sea beyond the mountains which 

 was always calm, he it was who first of white men saw the 

 Pacific and stood " silent upon a peak in Darien." Superseded 

 by an incompetent and unscrupulous gold-seeker, who had 

 influence at Court, Nunez was nevertheless allowed to devote 

 the remainder of his life to building ships on the western 

 coast of the Isthmus for the exploration of the new ocean. 

 Materials were brought from Cuba and dragged with infinite 

 labour through the forest and over the mountains. But when 

 he was ready with three hundred men to launch his four 

 ships, he was " judicially " murdered by Pizarro and the 

 rapacious Pedrarias. With the ships of Nunez, Pedrarias 

 explored the coasts of Panama and Nicaragua. Nunez it was 

 who rendered possible the invasion of Chile and Peru. Had 

 he lived the conquest of the Incas had been earlier, and its 

 story had been different. 



GEOLOGY. 



By G. W. Tyrrell, A.R.C.Sc, F.G.S. 



THE CONCEALED COALFIELD OF YORKSHIRE 

 AND NOTTINGHAMSHIRE.— The proving of the concealed 

 coalfield to the east of the Permian escarpment which runs 

 from Nottingham along the boundary of the visible coalfield 

 into Yorkshire and Durham began in 1854, when the Duke of 

 Newcastle sank two pits at Shireoaks. Here the valuable 

 Top Hard Coal was obtained at a depth of one thousand five 

 hundred and thirty feet, and was found to be three feet ten 

 inches in thickness. By far the greatest progress in the 

 exploration of the concealed field, however, has been made 

 since the beginning of the present century. The chief areas 

 in which borings and shafts have been sunk are three in 

 number : one, to the south of Nottingham, has been developed 

 with a view to the London market ; a large area has been 



proved in the central region between Nottingham and 

 Gainsborough, near the navigable Trent ; but the largest 

 development has been made in the Doncaster district, where 

 special transport facilities are available. The amount of 

 information thus gained has become so large and valuable 

 that it has become necessary to collect and summarise it in a 

 publication of the Geological Survey, which has been written 

 by Dr. Walcot Gibson. 



The Nottingham and Yorkshire Coalfield is of the shape of 

 a basin, of which only the western rim is visible at the surface, 

 the remainder being concealed beneath successive sheets of 

 newer formations to the east. The eastern edge of the 

 concealed portion of the basin has not been reached in any of 

 the borings yet made. A thickness of about four thousand 

 feet of Coal Measures has been proved. Two borings each 

 end respectively in the Upper and Lower Coal Measures; all 

 the other borings and shafts end in the Middle Coal Measures. 



The chief conditions which affect the accessibility of the 

 coal in the concealed area are the thickness of the overlying 

 strata ; the configuration, structure, and folding of the Coal 

 Measures ; and the amount of denudation, if any, suffered by 

 the latter before the deposition of the Permian. Where direct 

 observation is possible it has been found that the Permian 

 rests unconformably upon an even surface of the Carboni- 

 ferous rocks, so smooth that a well-known graphic method 

 has been applied to contour the surface of the hidden Coal 

 Measures. The contour lines thus obtained are strikingly 

 parallel, and show that the buried surface has a remarkably 

 uniform slope directed a little to the north of east, and oblique 

 to the north-west strike of the Coal Measures. Hence higher 

 horizons in the Coal Measures tend to occur beneath the 

 Permian cover than at the outcrop. At Kelham and Thorne, 

 however, borings have shown that the Coal Measures rise, at 

 least locally, on approaching the Trent ; and if the general 

 slope of the buried surface (ninety to one hundred feet per mile) 

 is maintained here, the whole of the Coal Measures will be cut 

 out by the newer formations. The area of the concealed 

 coalfield already proved amounts to one thousand two hundred 

 square miles. 



ORIGIN OF TURQUOISE.— A theory of the origin of 

 turquoise has been propounded by S. Paige (" Economic 

 Geology," 1912, 382-92) to account for an occurrence of this 

 gemstone in the Burro Mountains of New Mexico. The 

 country rock is a Pre-Cambrian granitic complex, which has 

 been intruded by quartz-monzonite with intense fracturing 

 and mineralisation. The turquoise occurs in small veins 

 within both the igneous rocks, and the veins are closely related 

 to the surfaces of denudation. The author believes that the 

 turquoise was formed by the oxidation of copper sulphides 

 and pyrite in the zone of weathering, and the reaction of the 

 resulting solutions with apatite. The latter would supply the 

 necessary phosphorus to combine with the copper and 

 aluminium of the solutions and thus form turquoise. 



AN ENGLISH DESERT— The Long Valley, Aldershot. 

 is described by Alan G. Ogilvie in the June Geographical 

 Journal as an area which exhibits many of the phenomena 

 characteristic of deserts. The desert features, however, are 

 not due to aridity, but to the ceaseless erosion effected by the 

 hoofs and wheels of cavalry and artillery. This action has 

 completely stripped the area of the original mat of vegetation, 

 and has exposed the underlying sand and gravel to very rapid 

 erosion. The Long Valley is now dissected by a system of 

 stream -courses which reproduce all the essential features of 

 desert wadys. These are only filled after heavy rain, and 

 then contain rushing torrents which carry down large masses 

 of sand and gravel. Ordinary rain showers have no effect, as 

 the water percolates at once through the sand. Similarly the 

 water from a continuous spring loses itself in the sand after 

 running in a well-formed valley for about a hundred yards. 

 The erosion due to wind is, however, more important than 

 that of water. The wind is producing a steady lowering of 

 the surface of the valley by blowing away the lighter particles. 

 The finer dust is probably carried beyond the confines of the 

 area, but the blown sand tends to form miniature dunes on its 



