15S DAVEMPORT ACADEMY OF XATURAL SCIENCES. 



zig-zag, gracilis, Icevissimus. monodontus, and the various species of 

 Anodon. Tiiis, however, might be expected, as thej^ are so frail that 

 when the epidermis is decayed, thej' will soon crumble in pieces, and it 

 appears probable that a considerable portion of the minute fragments, of 

 which we find a great quantity, are the fragments of these thin shells. 



I have found the following TJniones, and about in the following order of 

 abundance, viz : Vnio pustidosus, verrucosus, metanevrus, plicatus, ceso- 

 pu-'i, cornutus, ligamentinus, ellipsis, gibbosus, crassidens and trigonus. Sev- 

 eral species would be very difficult to distinguish when weathered and de- 

 composed, e. g. — anodontoides from rectus, asperrimus,elegans, etc. In ad- 

 dition to these, of the larger aquatic univalves, Melantho subsolida is 

 usually abundant, and the Vivipara sidjpurpurea is not uncommon in the 

 Rock Island beds, and the larger land snails. Helix profunda, tliyroides, 

 riiultilineata and alternata are very numerous. All this seems to indicate 

 very positively that the molluscan fauna of this region has not mate- 

 rially changed in character since the formation of these shell strata. In 

 rather rare instances relics of the work of human hands have been found 

 associated with the shells. 



In about the middle of the shell-bed at East Davenport I found, in 

 May, 1870, the bone awl figured in Vol. I, Plate VII, fig. 7, and some 

 animal teeth, perhaps those of the deer, and a stone ax was said to have 

 been found, not long previovis, in a similar position, by one of the work- 

 men on the road, in digging near the same spot. Also, about midway in 

 the depth of the regular layer on the Island, I have found two " hammer- 

 stones'- in place, and recently a grooved stone axe in the upper edge of 

 the same bed. 



Mr. Tiffany found, some years ago, in the same shell layer, seventy-five 

 centimeters below the surface, a bone from the head of the ox or the 

 cow, over the left eye, exhibiting cuts made with an axe or some such 

 smooth, sharp instrument, indicating that the deposit does not date prior 

 to the use of iron or steel instruments, and the introduction of domestic 

 cattle. 



Prof. Sheldon has also found several fragments of bones of some of the 

 larger animals, perhaps the deer, one of which has been fashioned into 

 an awl, similar to the one from East Davenport; also some very small 

 bones, one of which, probably a bone of some bird, has evidently been 

 cut off with some cutting tool. He also found there a few fish bones and 

 one anow head. 



A NATURAL DEPOSIT. 



If these shell beds have not accumulated as refuse heaps, of course 

 they are not to be considered as the work of human hands at all, as no 

 other occasion or method has, so far as I am aware, ever been assigned 

 for the intentional or unintentional collection of such quantities of shells. 

 That they are not of such artificial character is, I think, clearly indicated 

 by the following considerations, viz : 



First. The beds are frequently of considerable extent and thickness, 

 showing that a long time must have been required for a refuse heap to 



