ON THE MOVEMENTS OK THH EARTH'h CRUST. 327 



the winter falls in aphelion or perihelion, and aciiordinii' as the eccen- 

 tricity of the earth's orbit is small or great. 



Such an alteration in the strength of the marine currents will pro- 

 duce an alteration of the climate, which however will not be very im- 

 l)ortant, but which will nevertheless be great enough to leave its traces 

 in the deposits. During colder and drier seasons the streams are fed in 

 great part by spring water. This water has drained slowly through 

 the beds and is charged with dissolved materials; but the small quan- 

 tity of water and the feebler streams carry less clay, sand, and gravel. 

 During rainy seasons, the rain carries down quantities ol" such materi- 

 als, but it Hows off rapidly, and as it for the most part runs only over 

 the surface it has not time to dissolve so much. Although the springs 

 flow more abundantly during rainy seasons, their water only mingles 

 with the rain-water. The streams are therefore poorer in dissolved 

 material, but they contain more water, and their more powerful current 

 carries more clay, sand, and gravel into the basin. Hence the drier 

 seasons will be richer in purely chemical deposits, which will be trans- 

 ported in tiie clearer water; the wet seasons in mechanical deposits. 

 Strata of both kinds are formed, of course, at all times, but they are 

 deposited at different places in accordance with the xariatioji in tbe 

 (luantity of rain. Thus, I assume that when thick deposits of river- 

 sand and clay alternate with each other, when soft clay and marl alter- 

 nate with hard marl or liniestone, when thick strata of loose sand alter- 

 nate with sandstone, which is bound together by chemically produced 

 cement (iron, silica, lime), when clay alternates with Septaria-beds, etc., 

 then, in each case, the ftrst-named deposit shows itself to belong to 

 seasons with a warmer sea and a greater quantity of rain, whi(;h, as 

 regards western Europe, will mean seasons with the winter in ai)lielion. 



That this alternation of deposits implies a period of several thousand 

 years' duration is shown by the fact that the fossils change rapidly 

 through the strata. In the Tertiary formations there are only a few, 

 often only four to five, such changes of dei)osits in each stage. The 

 whole Oligocene period has only about thirty, the Miocene still fewer, 

 and the Pliocene barely twenty such changes. 



In this way, in my opinion, the precessions stamp themselves upon 

 the strata, and this should theretbre furnish a means of measuring 

 time. The greater the eccentricity of the orbit, the more strongly 

 marked will the periods be ; when the orbit approaches the circular 

 form, they are less recognizable.* 



* But tbo perihelion also sliifts to and fro. The time between two aphelia in the 

 winter solstice varied thus in post-glacial times by fnlly 4()00 years. This must have 

 some inlliience. The longer a period with winters in aphelion lasts the longer will 

 the warm cnrrents in the Atlantic increase in strength, and the greater will be the 

 changes of climate. The mild period during which Bergenian sea-animals lived in 

 the Christiania Fjord, and which has left its traces elsewhere in our hemispht^re, was 

 in my opinion, a conse(|uence of such an unusually long period with the winter in 



