50 



contents may appropriately, within limits, be taken as indicative of the 

 condition of that population at the times when the respective strata were 

 being deposited. 



To make clear the succession 

 of the strata in the shell-heaps, 1 

 subjoin an ideal section of one of 

 them, with one of the house-pits 

 of a subsequent village surmount- 

 section of shell-heap. ^"^ '^'^ ^^^^ section showing the 



A. Original hardpaD. stouc-walls of the Ijittcr Still in 



B. Ecbiniis layer. 1 , , i , i • <• 



c. Fisbbone layer. placB beneath the covering ot 



D. Mammalian layer. .11 i i i i - 7 • 



E. MoJern deposits and vegetable mold. Vegetable mOld aud (ICUnS. 



A.— THE LITTORAL PERIOD. 



In most of our excavations, especially in Attu, Amchitka, and Adakh, 

 we found the first stratum of the shell-heaps, above the primeval soil or 

 hardpan, to be composed almost exclusively of the broken test and spines 

 of Echinus {Strongylocentrotus) BrobacMensis, (Miill.) Agassiz, recently 

 described by E. Perrier under the name of LoxecMnus violaceus. This 

 is a.t present the common and only species of the family found living 

 in the Aleutians. With it were found sparingly the shells of the following 

 edible mollusks, all found living in the adjacent waters at the present time: 



Modiola vulgaris, Fleming. 



Mytilus edulis, Lin. 



Purpura lima, Martyn. 



Purpura decemcostafa, Mid. 



Litorina sithana, Phil, and vars. 



Tapes staminea, Cour. 



Saxidomus squalidus, Desh. 



Macoma nasuta, Conr. 



Acmfca patina and A. pelta, Esch. 



The list is given in the order of the frequency of their occm-rence, but 

 they do not form altogether more than one-tenth of one per centum of the 



