292 TROPICAL NATURE, AND OTHER ESSAYS. 



how could these coexist on a mere speck of land wholly 

 cut off from the rest of the world ? Mr. Mott maintains 

 that these facts necessarily imply the power of regular 

 communication with larger islands or a continent, the arts 

 of navigation, and a civilisation much higher than now 

 exists in any part of the Pacific. Very similar remains 

 in other islands scattered widely over the Pacific add 

 weight to this argument. 



North American Earthworks. — The next example is 

 that of the ancient mounds and earthworks of the North 

 American continent, the bearing of which is even more 

 significant. Over the greater part of the extensive Missis- 

 sippi valley, four well-marked classes of these earthworks 

 occur. Some are camps, or works of defence, situated on 

 bluffs, promontories, or isolated hills ; others are vast 

 in closures in the plains and lowlands, often of geo- 

 metric forms, and having attached to them roadways 

 or avenues often miles in length ; a third are mounds 

 corresponding to our tumuli, often seventy to ninety 

 feet high, and some of them covering acres of ground ; 

 while a fourth group consists of representations of 

 various animals modelled in relief on a gigantic scale, 

 and occurring chiefly in an area somewhat to the north- 

 west of the other classes, in the plains of Wisconsin. 



The first class — the camps or fortified inclosures — 

 resemble in general features the ancient camps of our 

 own islands, but far surpass them in extent. Fort Hill, 

 in Ohio, is surrounded by a wall and ditch a mile and a 

 half in length, part of the way cut through solid rock. 

 Artificial reservoirs for water were made within it, while 

 at one extremity, on a more elevated point, a keep is 

 constructed with its separate defences and water- 



