96 PEOP. J. LOGAN LOBLEY, F.G.S.^ F.E.G.S., ON 



the amount of the time during which these changes have taken 

 place is the frame, so to speak, of the picture that contains all 

 the details of the whole. The magnitude of that frame must 

 therefore be known before we can fairly judge of the factors 

 that have produced the components of the picture. 



It is now but a common-place to speak of geological time as 

 vast, although only half a century ago this great fact was most 

 warmly and obstinately disputed. But though an enormous 

 period is now undisputed, its duration can only be realised by 

 those who have paid some attention to the details of geological 

 science. The facts establishing the very high antiquity of the 

 earth are so many, so striking, and so certain, that the conclusion 

 is obvious, and yet that conclusion is often overlooked. Only 

 a few of these facts can be noticed here, and these very briefly. 



The enormous thickness of the sedimentary rocks, averaging at 

 least 50,000 feet,* at once requires us to allow for their formation 

 as accumulated deposits a vast period of time. When further it 

 is found that these accumulations of sediment constitute -f-^ of 

 the land area of the globe, or 50,000,000 square miles, giving 

 500,000,000 cubic miles of accumulated detrital matter, we are 

 compelled to greatly extend our conception of geological time, 

 even if we allow a much more rapid destruction of surface 

 rocks and deposition of their detritus, throughout geological 

 time, than now. But careful examination of the rocks, even of 

 Pre-Cambrian rocks, gives no evidence of more rapid destruction 

 and deposition in the past than at present. " One of the very 

 oldest formations of Western Europe, the Torridon Sandstone 

 of North West Scotland," Sir Archibald Geikie says, " presents 

 us with a picture of long-continued sedimentation, such as may 

 be seen in progress now round the shores of many a mountain- 

 girdled lake. In that venerable deposit the enclosed pebbles 

 are not mere angular blocks and chips, swept by a sudden flood 

 or destructive tide from off the surface of the land, and huddled 

 together in confused heaps over the floor of the sea. They have 

 been rounded and polished by the quiet operation of running 

 water, as stones are rounded and polished now in the channels 

 of brooks or on the shores of lake and sea. They have been laid 

 gently down above each other, layer over layer, with .fine sand 

 sifted in between them. So trancpiil were the waters in which 

 these sediments accumulated, that their gentle currents and 

 oscillations sufficed to ripple the sandy floor, to arrange the 



* The aggregate maximum thickness of the sedimentary rocks is fully 

 260,000 feet. 



