164 PROGRESS OF SCIENCE. 



by demonstrating the relationship which exists between the 

 different parts of our planet, and the influence of the earth's 

 surface upon the development of humanity. 



1785 1873. Sedgwick was the first to notice the sepa- 

 rate nature of the CAMBRIAN ROCKS underlying the Lower 

 Silurian, and in a comprehensive survey tried to co-ordinate 

 the whole range of geological facts known in his time. He 

 mapped the geology of Wales ; described the PALAEOZOIC 

 (ancient life) DEPOSITS in detail, strongly opposing the 

 theories of derivation. 



17871856. Prevost established the theory of the 

 geological strata being formed by alternate FLUVIAL AND 

 MARINE DEPOSITS in the same basin by the meeting of 

 sea and river currents. 



1790 1852. Mantell, in the midst of a busy professional 

 life, carried on almost continuous geological explorations, in 

 the course of which he elucidated several interesting points 

 of the earth's history especially studying, with Buckland, 

 the Carboniferous, Wealden, and Tertiary deposits ; discovered 

 the bones of four out of the five great DlNOSAURlANS known 

 up to 1870, and among them the Iguanodon and the Hylaeo- 

 saurus thereby rendering signal service to palaeontology as 

 well as to geology. It may be said of him that if he left 

 scientific interpretations to Cuvier and Owen, he supplied the 

 two great masters with facts to work upon. He should also 

 be remembered as a popular expositor ; his " Medals of 

 Creation," " Wonders of Geology," " Petrifactions and their 

 Teaching," exercised great influence and aroused keen interest 

 in science. 



1792 1871. Murchison found the primitive rocks of 

 Wales to belong to a unique system THE SILURIAN ; 

 assimilated the stratified rocks of Devon and Cornwall to the 

 red sandstone of Scotland,* calling them the DEVONIAN 



* In his classification of rocks in the Scotch Highlands, Murchison, it 

 should be stated, made a serious mistake, which remained unnoticed for 

 a whole generation until it was overthrown by the observations of Pro- 

 fessors Nicol, Bonney, Drs. Charles Callaway, Henry Hicks, Mr. Hudle- 

 ston, and by the patient investigations of Mr. Charles Lapworth, a private 



