HYDROGRAPHY, PAST AND PRESENT. 229 



be nearly doubled, or about 1200 feet ; in other words, tbe lower members 

 of tbe true Coal-measure formation may be fairly expected to occur at 

 about that distance south from the corner of Tottenham Court Road and 

 Oxford Street, the upper, or productive Coal measure, still farther to the 

 south. 



What has been ascertained beyond all doubt as to the line of section 

 underlying a part of our English area from London to Ware, may be 

 safely taken as holding good for a great extent of country on the east as 

 on the west. The ages of more modern overlying formations do not affect 

 this question, as is shown by the borings here in England, but more 

 abundantly on the European continent. In our attempts to trace accu- 

 rately hidden physical arrangements of the earth's crust, the restrictions 

 to be observed are the positive data of the ascertained thicknesses of the 

 several formations, and their positions, and which enable us to replace, 

 without much chance of error, the line of each band and of its direc- 

 tion of dip. 



Hydrography, Past and Present 

 By Lieutenant Gr. T. Temple, R.K, F.R.G.S. 



[A communication ordered by the General Committee to be printed 

 in externa among the Keports.] 



[Plate XV.] 



The immediate aim of this paper is to bring to the notice of the section 

 the present state of hydrographical science, which forms an essential part 

 of the machinery by which our enormous commerce is carried on in time 

 of peace, and defended during war. The subject is therefore of great 

 national importance, and I sincerely trust that it will meet with your 

 favourable consideration. 



In the annual address to the Royal Geographical Society, the unsatis- 

 factory state of the Admiralty charts for South Africa was pointed out by 

 our President, Mr. Clements Markham, whose unremitting devotion to the 

 advancement of geographical science is well known to most of those 

 present. He observed that the war in Zulu-Land had called public 

 attention to the unsurveyed state of parts of the coast of South Africa, 

 H.M. Ships Active and Tenedos having been placed in great danger 

 through grounding on some unknown reefs between the Tugela River 

 and Point Durnford. He told us also that both the east and west coasts 

 of South Africa (northwards from Bashee River on one side, and 

 St. Helena Bay on the other) have not been sounded since the days of 

 Captain Owen, half a century ago. This must have been a startling 

 announcement to those who fancy that we already know the world 

 perfectly, and who are not aware that the outlines given on the beautiful 

 maps of Keith Johnston and others are, to a great extent, mere guess- 

 work. It was, however, well known to the few who for some years past 

 have been steadfastly working to restore the surveying branch of the 

 Uavy to the high position it formerly held. 



The story of this essential branch of the public service, which has 

 been characterised as ' not only useful in peace, but terrible in war,' is 

 •a curious illustration of the difficulties attending the construction and 



•e 



