9$ THE STORY OF THE EARTH. 



The carboniferous period, like the preceding 

 - evidence of conditions which are in 

 part marine, and in part terrestrial. In the south- 

 ern area, it is the marine condition which is chiefly 



eloped ill the lower part of the formation. 

 Whereas, ill the northern area, terrestrial condi- 

 tions are developed towards the base. In travel- 

 ling southward from Scotland over Britain the 

 terrestrial beds come to hold a higher and higher 

 position among the carboniferous strata. The 

 formation is usually taken to include four or five 

 chief divisions, which, commencing at the base, 

 are reckoned as Lower Limestone Shales, Car- 

 boniferous Limestone, Yoredale beds, Millstone 

 grit and Coal Measures. 



The first point Of interest of this epoch, is in 



the circumstance that in Scotland, the Calciferous 



Sandstone, which attains a thickness of 3,50c f 



at the base of the formation, so that the sand- 

 ie conditions o( the carboniferous period, suc- 

 ceed to the sandstone conditions of the old red 

 There arc occasional beds of lime- 

 stone and shales, like the Lurdiehouse limest 

 in the upper part of the group. The fossils in- 

 clude land plants. There 1- evidence of consider- 



tivity, especially in the tuffs and 



andesite lavas associated with the calciferous pe- 

 riod, in the Carlton 1 1 ills, north of Haddington. 

 In the shale r tWO COal seams; and the 



< unetimes so bituminoi;- 

 to be a valuable mineral oil. The tcr- 



trial conditions, which commenced in this way 



never to have entirely cuv: 

 in any 1 IS in w huh the coal is found. 



,: break in £ d in 



of physical conditions with the older 



