xxr.] THE SUN. 377 



withheld. Without the heat which is derived from the sun, 

 the temperature of the earth would fall far below the limit 

 at which life can be sustained. Green plants decompose 

 carbonic acid, and obtain their supply of carbon, only 

 under the influence of sunshine; and, it has often been 

 remarked, that our stores of coal represent so much sun- 

 shine of the Carboniferous period. Nor is this a mere 

 wild fancy ; for without the sun there would certainly have 

 been no coal. 



In studying the geological structure of the Thames basin, 

 it was shown that the country had experienced great changes 

 of climate at different periods of its history ; and such 

 changes depend entirely upon our varying relations with the 

 sun. In fact, without the sun, the Thames could have had 

 no geological history ; for the upper beds, out of which its 

 basin is shaped, are almost exclusively made up of fragments 

 which have been worn from pre-existing land by means of 

 running water; and the flow of water must be connected, 

 directly or indirectly, with the action of the sun. 



And thus we reach, at last, the goal of our inquiry. At 

 the furthest point to which we have pushed our analysis 

 of the causes of the phenomena presented to us, the sun is 

 revealed as the grand prime mover in all that circulation 

 of matter which goes on, and has gone on for untold ages, 

 within the basin of the Thames ; and the spectacle of the 

 ebb and flow of the tide, under London Bridge, from which 

 we started, proves to be a symbol of the working of forces 

 which extend from planet to planet, and from star to star, 

 throughout the universe. 



