ADDKESS. 1 7 



strata lying above the chalk and below the carboniferous limestone re- 

 spectively, remained in a state of the greatest confusion. The year 1831 

 marks the period of the commencement of the joint labours of Sedgwick 

 and Murchisou, which resulted in the establishment of the Cambrian, 

 Silurian, and Devonian systems. Our Pre- Cambrian strata have recently 

 been divided by Hicks into four great groups of immense thickness, 

 and implying a great lapse of time ; but no fossils have yet been 

 discovered in them. Lyell's classification of the Tertiary deposits : the 

 result of the studies which he carried on with the assistance of Deshayes 

 and others, was published in the third volume of the ' Principles of 

 Geology' in 1833. The establishment of Lyell's divisions of Eocene, 

 Miocene, and Pliocene, was the starting-point of a most important series 

 of investigations by Prestwich and others of these younger deposits ; as 

 well as of the post-tertiary, quaternary, or drift beds, which are of special 

 interest from the light they have thrown on the early history of man. 



A full and admirable account of what has recently been accomplished 

 in this department of science, especially as regards the palasozoic rocks, 

 will be found in Etheridge's late address to the Geological Society. 



The thickness of the sedimentary strata implies an enormous lapse of 

 time, but the amount of subsequent destruction which has taken place is 

 scai'cely less surprising. Ramsay, for instance, has shown that in Wales 

 from 9,000 to 11,000 feet of solid rock have been removed from largo 

 tracts of country. Faults or cracks there esteud for miles, with the strata 

 on one side raised in some cases as much as 10,000 feet above the same 

 strata on the other, and yet there is not on the sui'face the slightest 

 vestige of this gigantic dislocation. 



The long lines of escarpment again, which stretch for miles across our 

 country, and were long supposed to be ancient coast lines, are now ascer- 

 tained, mainly through the researches of Whitaker, to be due to the dif- 

 ferential action of aerial causes. 



Before 1831 the only geological maps of this country were William 

 Smith's general and county maps, published between the years 1815 and 

 1821!. In the year 1832 De la Beche made proposals to the Board of 

 Ordnance to color the ordnance-maps geologically, and a sum of 300Z. was 

 granted for the purpose. Out of this small beginning grew the important 

 work of the Geological Survey. 



The cause of slaty cleavage had long been one of the great difhculties 

 of geology. Sedgwick suggested that it was produced by the action of 

 ci'ystalline or polar forces. According to this view miles and miles of 

 country, comprising great mountain masses, were neither more nor less 

 than parts of a gigantic crystal. Sharpe, however, called attention tu 

 the fact that shells and other fossils contained in slate rocks are com- 

 pressed in a direction at right angles to the planes of cleavage, as if the 

 rocks had been seized in the jaws of a gigantic vice. Sorby first maintained 

 that the cleavage itself was due to pressure. He observed slate rocks con- 

 taining small plates of mica, and that the effect of pressure would tend to 

 1881. c 



