264 SIB CHARLES LYELL. 



at least thirty-five thousand years have passed 

 since the river began to cut its passage between 

 the high rocky walls. " What would I give," said 

 Lyell, " for a daguerrotype of the scene as it was 

 four thousand, and again forty thousand years ago ! 

 Even four centuries would have been very impor- 

 tant." Authorities differ as to the rate of the 

 recession of the falls. Some estimate an inch 

 instead of a foot yearly, requiring a period of 

 more than four hundred thousand years. 



In 1845, Lyell published his "Travels in North 

 America, with Geological Observations," and in 

 September of the same year, returned again to the 

 States, spending nine months in travel and study, 

 and bringing out later, in 1849, his " Second Visit 

 to the United States of North America." 



Already his "Elements of Geology" had ap- 

 peared, which went through several editions. A 

 seventh edition of the " Principles " had been 

 published. He had also been knighted by the 

 Queen, for his rare scholarship. Honored at home 

 and abroad, working ardently and earnestly, often 

 with failing sight, he had already won for himself 

 the eminence of which he had dared to dream 

 years before. 



Of course he was welcomed at all great gather- 

 ings. Macaulay and Hallam, Milmore and Mrs. 

 Somerville, Rogers, and scores of others were often 

 at his home. 



In 1851, he was appointed one of the Royal Com- 

 missioners for the first Great Exhibition held in 



