MACKIE — REMNANTS OF THE FIRST LIFE-WORLD. 137 



table of rock-groups, page 64, and the ideal diagramatic section at 

 page 93, will already have done something towards this, but the more 

 detailed view and remarks I am now about to add will still more ex- 

 plicitly convey a correct idea of our starting point and its relations to 

 these early deposits by which it was succeeded. 



OLD RED SANDSTONE. 



UPPER 

 SILURIAN. 



LOWER 

 SILURIAN, 



LUDLOW ROCKS. 

 WENLOCK ROCKS, 



(including the Woolhope Limestone 

 and Denbigh Grits and Shales.) 



UPPER CARADOC. ( Beds of 



May Hill and Llandovery Beds. ( Passage. 



LOWER CARADOC, 



Caer Caradoc and Bala Hocks. 



LLANDEILO ROCKS. 



BOTTOM ROCKS 



Cambrian 

 of 



Sedgwick. 



(Cambrian of Murchison, and of the 

 Geological Survey, but only a part of 

 the Cambrian of Sedgwick), 

 reposing on 



GNEISS— FUNDAMENTAL ROCKS— GRANITE. 



Between the fundamental gneiss and granite and the lowermost 

 beds of the Silurian formation are mountains of strata, about which, 

 except for their mineral, domestic, or commercial value, little is 

 generally known. Their accumulated thickness is calculated by 

 thousands of feet, and they were formerly styled by geologists Azoic, 

 under the belief that they contained no organic remains, and that they 

 were formed before the dawn of life upon our globe. These are the 

 " Bottom Rocks," which form the subject of this chapter. 



{To he continued.) 



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