298 ANNUAL OF SCIENTIFIC DISCOVERY. 



of unmodified drift; and indeed we might say the same of a considerable 

 part of the period of the modified drift and alluvium." 



12. Glaciers probably existed on the mountain summits that stood above 

 the waters, as facts appear to show. 



13. The apparent elevation of the continent may have been a consequence 

 of an actual sinking of the bed of the ocean, drawing away the waters from 

 the land. 



14. The drift scratches, and transportations of stone, gravel, etc., were pro- 

 duced mainly by icebergs during a period of continental submergence. 



THE GEOGRAPHICAL DISTRIBUTION OF LAKES, CATARACTS, AND 

 NAVIGABLE RIVERS. BY DANIEL VAUGHAN. 



Though lakes are very numerous in the Eastern States and in British 

 America, they are almost entirely absent from the part of our continent 

 included between the Atlantic Ocean and the Rocky Mountains, and between 

 the thirty-first and thirty-second parallels of north latitute. This region 

 contains over a million and a half of square miles ; and the territory of 

 Brazil, which is about double the extent, exhibits, in like manner, an 

 absence of any large collections of fresh water. But both these regions are 

 distinguished for their smooth streams and navigable rivers, which are un- 

 equalled in the advantages they afford for inland communication. France 

 contains no lakes and no waterfalls of any magnitude, but its rivers are well 

 suited for navigation ; while, in Sweden and the State of Maine, lakes are 

 numerous, and the rivers are so much interrupted by cataracts that they 

 cannot be navigated to any considerable extent, even by the smallest 

 vessels. 



The fact that rivers are most free from cataracts and best suited for navi- 

 gation, in regions where there are no lakes, is an evidence that running 

 waters take a considerable part in forming channels for themselves. After 

 one or two thousand centuries, most of the cataracts of Sweden, of Maine, 

 and of British America, will be obliterated ; their lakes will be drained or 

 silted up, and their rivers, being cleared of impediments, will be well adapted 

 to the purposes of navigation. Such changes have been produced in other 

 lands during geological times. On several of the rivers of France and Spain, 

 geologists have discovered the sites of ancient lakes, which have long since 

 disappeared by aqueous action. It would seem also that, in former times, 

 the Alleghany mountains enclosed many sheets of fresh water, similar to 

 those found in the Alpine valleys, or between the Scandinavian mountains. 

 Could we fill up all the channels of erosion, and deep ravines through which 

 rivers flow, their waters should cover a large part of the land; and we may, 

 therefore, infer, that lakes and cascades must have diversified the scenery of 

 all regions, at some period of their geological history. 



We may, therefore, regard the presence of numerous lakes and cataracts 

 as an indication that the regions where they occur have been only recently 

 elevated, and that they have not been long free from the effects of subterra- 

 nean violence; while smooth streams and navigable rivers are an evidence 

 of the great age of the lands where they are found, and show that they have 

 been long released from the dominion of the waves 



