32 CHARLES DARWIN. 



the valley. At the time Darwin studied them, the 

 terraces were believed to have been formed by a lake 

 dammed back by a barrier of rock and alluvium ; 

 this he proved to be wrong, and as no other barrier 

 was then available for the evidences of glaciation 

 had not then been discovered by Agassiz he was 

 driven, on the method of exclusion, to the action of 

 the sea. Upon this subject he says, in the " Auto- 

 biography," "My error has been a good lesson to 

 me never to trust in science to the principle of 

 exclusion." 



On January 29th, 1839, he married his cousin,, 

 Emma Wedgwood, the daughter of Josiah Wedgwood, 

 of Maer. They resided at 12, Upper Gower Street 

 until September 14th, 1842, when they settled at 

 Down. 



The few graceful and touching words in which 

 Francis Darwin, in the " Life and Letters," alludes to 

 his father's married life show how deep is the debt of 

 gratitude which the world owes to Mrs. Darwin ; for 

 without her constant and loving care it would have 

 been impossible for Darwin to have accomplished his 

 life-work. 



During these years in London his health broke 

 down many times ; so that he says, in the " Auto- 

 biography " : "I did less scientific work, though I 

 worked as hard as I possibly could, than during any 

 other equal length of time in my life." He chiefly 

 worked at his book on "The Structure and Distri- 

 bution of Coral Reefs," published in 1842 (second 



