S POPULAR GEOLOGT. 



that they are arraQged in a regular systematic order. The rocks are not 

 mere patches, for some extend in a continuous line for hundreds of miles. 

 The coal-measures of the North of England, for instance, extend from 

 Northumberland to Derbyshire, and the chalk rocks from Flambro' Head 

 to Kent, and thence across the country to the Bristol Channel. If we walk 

 over the country from Halifax to the east coast, after leaving behind sand- 

 stone rock and coal strata, we shall pass over new red sandstone, then lias 

 marls and oolite, and arrive at Flambro' Head, on the chalk rocks. If we 

 go from Halifax to Cumberland, after passing over moorlands of grit and 

 shale, and over the limestone rocks of Craven or Clitheroe, and the old red 

 sandstone of Westmoreland, Ave arrive at the slate and granite rocks of 

 Skiddaw. Here we see that the oldest rocks, such as granite, slate, and the 

 like, occupy the highest summits, and the others lie upon them in succes- 

 sion, one upon another, the youngest being last, and consequently the 

 uppermost. Generally speaking, the igneous rocks occupy the west and 

 north-west of England, and the oldest stratified rocks lie upon them, 

 occupying the middle of the country, while the east and south-east are 

 covered by the newer formations. This order of arrangement is never 

 inverted ; if, in any locality, we find one set of rocks under another set, we 

 never find them placed over them in any other place. For example, the 

 lower coal strata of North and Southowram lie upon the grit rocks of 

 Halifax, and are covered by the well-known flagstone rock. The same 

 order of arrangement has been observed at Leeds, Bradford, Sheffield, and 

 even in Lancashire. This is Avhat is meant by the term "succession of 

 rocks." As all the formations from the Silurian slate of Skiddaw to the 

 chalk rock of Flambro' Head contain marine shells of various species, "it 

 is evident that those found in the lowest formations belong to animals that 

 lived in an earlier stage of the world's history than those found in the 

 strata immediately above them; and so on through all the other successive 

 formations till we come to the chalk ; and if it should be found that in 

 some degree, or altogether, the shells of each formation are of species distinct 

 from those of any other formation, then by the* fossils alone we shall be able 

 to tell to what stage of the world's history these forms of life belong, and 

 a clue is thus obtained to the history of the succeasion of marine life of 

 the globe. This law is called "</je successufli of life in ti7ne," which, along 

 with the succession of strata, is the foundation upon which Geology is 



