WORKS O F ]J E F E N C E . 9 



To facilitate description, and to bring something like system out of the dis- 

 ordered materials before us, the enclosures are, to as great a degree as practicable, 

 divided into classes ; that is to say, such as are esteemed to be works of defence are 

 placed together, while those which are regarded as sacred, or of a doubtful 

 character, come under another division. 



WORKS OF DEFENCE, 



Those works which are incontestibly defensive usually occupy strong natural 

 positions ; and to understand fully their character, their capability for defence, and 

 the nature of their entrenchments, it is necessary to notice briefly the predominant 

 features of the country in which they occur. The valley of the Mississippi river, 

 from the AUeghanies to the ranges of the Rocky Mountains, is a vast sedimentary 

 basin, and owes its general aspect to the powerful agency of water. Its rivers - 

 have worn their valleys deep into a vast original plain ; leaving, in their gradual 

 subsidence, broad terraces, which mark the eras of their history. The edges of 

 the table lands, bordering on the valleys, are cut by a thousand ravines, presenting 

 bluft' headlands and high hills with level summits, sometimes connected by narrow 

 isthmuses with the original table, but occasionally entirely detached. The sides 

 of these elevations are generally steep, and difficult of access ; in some cases 

 precipitous and absolutely inaccessible. The natural strength of such positions, 

 and their susceptibility of defence, would certainly suggest them as the citadels of 

 a people having hostile neighbors, or pressed by invaders. Accordingly we are 

 not surprised at finding these heights occupied by strong and complicated works, 

 the design of which is no less indicated by their position than by their construction. 

 But in such cases, it is always to be observed, that they have been chosen with 

 great care, and that they possess peculiar strength, and have a special adaptation 

 for the purposes to which they were applied. They occupy the highest points of 

 land, and are never commanded from neighboring positions. While rugged and 

 steep on most sides, they have one or more points of comparatively easy approach, 

 in the protection of which the utmost skill of the builders seems to have been 

 exhausted. They are guarded by double, overlapping walls, or a series of them, 

 having sometimes an accompanying mound, designed perhaps for a look-out, and 

 corresponding to the barbican in the system of defence of the Britons of the middle 

 era. The usual defence is a simple embankment, thrown up along and a little 

 below the brow of the hill, varying in height and solidity, as the declivity is more 

 or less steep and difficult of access. 



Other defensive works occupy the peninsulas created by the rivers and large 



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