tlie Displacement of Shore-lines. 423 



by 5'6 m., and a double lengthening of the polar radius, 

 therefore, by 11*2 m. What value tlie lengthening of the 

 day had in Tertiary times we do not know. It cannot well 

 have been remarkably greater than in recent times. And it 

 seems therefore in any case to follow, as stated above, that 

 the vertical displacement of coast-lines can scarcely have been 

 in general more than a few metres under any oscillation, in 

 case our attempted explanation is correct. Therefore we must 

 now see whether the displacement of coast-lines was so very 

 considerable. 



We must first examine how much is deposited in each pre- 

 cessional period, and how great is the thickness of the stages. 

 The thickness of the deposit depends, in the first place, upon 

 the situation of the place, whether it lies near or far from the 

 land or the mouths of rivers, and upon the nature of the 

 deposit ; chemical deposits are commonly thinner than me- 

 chanical ones. As a mean number for each processional 

 period (20,000 to 21,000 years), I have obtained the following 

 values for the different kinds of alternating deposits : — 



Marl and siliceous limestone, from 0*6— 2*2 m. 

 Clay and siliceous limestone, 1*3 m. 

 Marl, gypsum, siliceous limestone, marine, 1'3-1"4 m. 

 Ditto, freshwater, 2'8-2'9 m. 

 Limestone and marl, l' 8-2*5 m. 



Marl, argillaceous limestone, ironstone, sandy marl, 2 m. 

 Sand, calcareous sandstone, marine, 2-2'3 m. 

 Ditto, freshAvater, 3 m. 



Sand, clay, ferruginous sandstone, marine, 5-6 m. 

 Clay, limestone, ironstone, sand, 5-7 m. 

 Sand, marly clay, ferruginous sandstone, lignite, up to 

 30-60 m. 



In each stage, when there has only been one oscillation of 

 the sea, there are usually 4 or 5 such alternating deposits ; so 

 the thickness of the stages is generally but small. I may cite 

 the following examples. First, from the Paris basin : — the 

 Calcaire Grossier, which represents 25 deposits and several 

 (5-6) oscillations, is only 31'5 m. thick ; Sables de Beau- 

 champ, 13—14 m. ; the Calcaire de St. Ouen, with 10 alternating 

 deposits, is only 6-7 m. ; marine gypsum, 16-17 m. ; palustrine 

 gypsum, 20 m. ; Sables d^Etampes, 11-12 m. 



In the Isle of Wight the beds are thicker, but also richer 

 in mechanical deposits : — Plastic Clay, 26 m. ; London Clay, 

 61 m. ; Lower Bagshot (sand, clay, lignite, and ferruginous 

 sandstone, with 7 alternating deposits), in all, 200 m. ; 

 Bracklesham, of the same kind as the preceding and without 



