334 THE POPULAR SCIENCE MONTELY. 



other acting as principal. In all the larger lakes there has evidently 

 been a local sinking of the surface, the glacier having been only- 

 auxiliary. The numerous small lakes in Middle and Western New 

 York lying in the direction of the glacier-flow, and having frequent 

 groovings on their adjacent walls, have been credited wholly to the 

 glacier. But, as nearly the whole of this lake-region lies within the 

 Niagara limestone formation, it is not improbable that the falling of 

 cave-roofs may have greatly aided the work of the ice-plow. Many 

 small lakes and ponds, as in Kentucky, Tennessee, and Southern 

 Indiana, are due wholly to the falling down of cave-roofs. In South- 

 Eastern Missouri and Eastern Arkansas are lakes and lakelets where 

 these roofs were shaken down by the earthquake of 1811. Lakes 

 Borgne and Pontchartrain have been captured from the Gulf by the 

 delta of the Mississippi ; while numerous small lakes, called bayous, 

 have been formed by changes in the river-bed, the deposit of sedi- 

 ment at both their inlets and outlets having kept them filled with 

 water. Crater-lakes are not infrequent. These basins, but containing 

 no water, abound in New Mexico, Arizona, and Southern California, 

 while many of the beautiful lakes of the Italian Peninsula are but the 

 filled craters of extinct volcanoes. 



"Why is the North the land of lakes? In order intelligently to 

 answer this question, let us see what has been going on at the South. 

 Between the Alleghanies and the Blue Ridge is a long, narrow valley 

 extending nearly the whole length of these parallel ranges ; and, but 

 for the breaks in whose walls, the whole extent must have been a 

 basin of water. At Harper's Ferry, the Potomac, and near the Natural 

 Bridge, the James River, have broken through the Blue Ridge carry- 

 ing the waters of the upper half of the valley to the Atlantic. Farther 

 to the south the Kanawha and the Tennessee drain the lower half into 

 the tributaries of the Gulf of Mexico. These last-named rivers have 

 also broken through the Cumberland Mountains, draining another con- 

 siderable valley between these and the Alleghanies. Could these sev- 

 eral outlets be closed, as they probably once were, large lakes would 

 again rapidly form, and the work of abrasion and drainage begin 

 anew. Could the Knobs and the Muldro Hills unite again at the falls 

 of the Ohio, a large shallow lake would form, covering parts of Ohio, 

 Indiana, and some of the fairest portions of Kentucky. Should the 

 bluffs of the "Wabash come together at the mouth of the Salimony, 

 another shallow lake would result, whose outlet would probably be 

 the Maumee. Commencing at Richmond, Indiana, itself situated in a 

 small lake-basin, and thence northeastwardly half-way across Ohio, is 

 a succession of shallow depressions once filled with water, and through 

 which still flow the streams whose unceasing work has cut through 

 their margins and emptied them of their contents. In many of these 

 ancient lake-basins the draining is not yet completed, the lowest parts 

 being still marshes or ponds of water. The Mohawk and the Con- 



