632 



HISTORICAL GEOLOGY 





Fig. 560. — Daemonhelix, Nebraska. 

 (Redrawn after E. H. Barbour.) 



and since they resist erosion 

 somewhat better than the sur- 

 rounding rock, they often stand 

 out prominently against the 

 bluffs. They have been con- 

 sidered the burrows of extinct 

 rodents and also fossil algae, but 

 the proof of the latter seems 

 now to be well established. 



Geological History of Se- 

 quoias. — The history of the 

 sequoias (big trees and red- 

 woods) of California is a strik- 

 ing example of the fate of many 

 animals and plants, and illustrates the difficulty of finding the 

 cause of extinction in plants as well as animals. These big trees, 

 which sometimes grow to a height of 325 feet, have a girth of 50 

 or 60 feet, and live to be 5000 years old, are now confined to the 

 mountain slopes of California. In the Tertiary the sequoias were 

 common trees in the northern hemisphere, extending from Spitz- 

 bergen (78 north latitude) as far south as the middle of Italy, in 

 Asia to the Sea of Japan, and over a large part of North America. 

 The sequoias date back to the Cretaceous, where they were un- 

 doubtedly represented by several species. " This is perhaps the most 

 remarkable record in the whole history of vegetation. The sequoias 

 are the giants of the conifers, the grandest representatives of the family, 

 and the fact that, after spreading over the whole northern hemisphere 

 and attaining to more than 20 specific forms, their decaying remnant 

 should now be confined to one limited region in western America and 

 to two species constitutes a sad memento of departed greatness. 

 The small remnant of Sequoia gigantea (the big trees) still, how- 

 ever, towers above all competitors, as eminently the " big trees," 

 but, had they and the allied species failed to escape the Tertiary con- 

 tinental submergences and the disasters of the Glacial Period, this 

 grand genus would have been to us an extinct type." (Dawson.) It 

 is stated that the sequoias were so abundant in northwest Canada 

 as to furnish much of the material for the great lignite beds of that 

 region. That the climate of other parts of the world is still suited 

 to the growth of these trees is shown by the fact that sequoias are 

 now growing in England and around Lake Geneva in Switzerland from 



