1847.] Association of Geologists and JVaturalists. 199 



and water- worn stones — under this is a fine loam, of a mottled 

 appearance, indicating the deposition of the different earths — then 

 a stratum of fine white sand — and thus alternating to the bottom, 

 where the loam rests on an altar: these strata are well defined, 

 though their arrangement is not always uniform: excavations will 

 always be found near by, from which the materials were obtained. 



They cover altars of burnt clay or stone, containing various im- 

 plements of ancient art. 



None are found on the first, or latest formed terraces of rivers, 

 excepting in the Mississippi valley. Very old trees are found 

 growing on them; they date back at least 1200 or 1000 years; 

 this is shown from the fact that they are covered by the same trees 

 as those of the surrounding forests; for when a spot has been 

 cleared of trees the next growth is of a different tree, and it is 

 only after a very long time that the primitive tree reappears 



In the mounds are found objects foreign to the region in which 

 they are situated; these are very interesting, as showing the state 

 of civilization, and the commercial intercourse of the mound- 

 builders. Obsidian is found in considerable quanity ; and as Central 

 Mexico is the nearest spot where it occurs abundantly, their mi- 

 grations must have been thus extended — native silver from Lake 

 Superior, pearls from the southern waters, and other objects from 

 very distant localities, are found; considerable quantities of galena; 

 the occurrence of gold is questionable; no iron is found, except 

 in the latest deposits, and it is certain that this ancient people 

 were unacquainted with it; axes, plates, and bracelets of copper, 

 and masses of the native unwrought copper are found; these 

 bracelets are identical in form with those of the ancient Eygpt- 

 ians. The implements are mostly of stone; the lance and arrow 

 heads of different varieties of quartz; the stone-axes are identical 

 with those found in Denmark, except in material; there are many 

 specimens of porphyry; great quantities of mica, cut into various 

 ornamental shapes; beads of marine shells; pearls; fossil teeth of 

 sharks, cetacea, etc.; carvmgs, true to nature, of almost every 

 living thing in the country, and of many non-indigenous animals; 

 carvings of the human head, resembling the ancient Peruvian. 



On the Structure of the Polypi, hy Prof Jlgassiz. 



Their anatomical structure presents peculiarities which bear 

 upon the Echinoderms. The little holes on the surface of Actinia, 

 are analagous to the w^ater holes on the surface of the Echino- 

 derms. The Echinoderms, though radiated, have a bilateral, sym- 

 metrical structure. In Actinia, the mouth is not circular, but 

 elongated, one end being the widest, where the undigested food 

 escapes. The young have fewer tentacles than the adult; there 



