340 ON THE MOVEMENTS OF THE EARTH'S CRUST. 



stant, the day, iu one hundred thousand years (the time which is on the 

 average occupied by an oscillation of the eccentricity) should become 

 ten seconds longer. Moreover, Thomson reckons only the marine tidal 

 wave. To this should now be added Darwin's "interior tide," his 

 "bodily tides," which I know no means of calculating. For many mill- 

 ions of years, when the moon was nearer and the tidal action consid- 

 erably stronger, the day also increased more rapidly. But nowadays 

 its increase is uudoubtedly much slower, and we can not expect great 

 general changes of level in a short time from this cause. 



To a lengthening of the day by ten seconds (according to Todd,*) 

 corresponds a shortening of the equatorial radius by 0.6 meters and a 

 double lengthening of the polar radius, therefore, by 11.2 meters. 

 What value the lengthening of the day had in Tertiary times we do not 

 know. It can not 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 

 genera more than a few meters uiuler any oscillation, in case our at- 

 tempted 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 precessional 

 period and how great is the thickness of the stages. Tlie 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 thin- 

 ner than mechanical ones. As a mean number for each pre(;essional 

 period (twenty to twenty-one thousand years), I have obtained the fol- 

 lowing values for the different kinds of alternating deposits: 



Marl and siliceous limestone, from O.G to 2.2 meters. 



Clay and siliceous limestone, 1.3 meters. 



Marl, gypsum, siliceous limestone, (marine,) 1.3 to 1.1 meters. 



Ditto, fresh water, 2.8 to 2.9 meters. 



Limestone and marl, 1.8 to 2.5 meters. 



Marl, argillaceous limestone, (ironstone,) sandy marl, 2 meters. 



Sand, calcareous sandstone, (marine,) 2 to 2.3 meters. 



Ditto, fresh water, 3 meters. 



Sand, clay, ferruginous sandstone, (marine,) to (5 meters. 



Clay, limestone, ironstone, sand, 5 to 7 meters. 



Sand, marly clay, ferruginous sandstone, lignite, up to 30 to HJO 

 meters. 

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

 there are usually four or five such alternating deposits, so the thick- 

 ness of the stages is generally but small. I may cite the following ex- 

 amples. First, from the Paris basin: The Calcaire Grossier, which 



"American Naturalist, 1883, vol. xvii. p. 18. (Or as stated, 1 miuute of daily 

 leiij-thening is eqnivaloiit to 110 feet of erjuatorial depression.) 



