58 



layer is so hard that a bar and j^ick-ax are required to disintegrate it. The 

 beds vary in thickness, being in different places from one to three feet in 

 depth, and at least two feet being about an average. This layer is well 

 developed at Attu, Kyska, Amchitka, Adakh, most places examined on 

 Amaknak Island, and in the various shell-heaps examined on the island of 

 Unalashka. To this period I refer also the lowest stratum excavated in a 

 remarkable cave situated on Amaknak Island, Captain's Bay, Unalashka. 

 A short account of our excavations in this cave (which we entirely cleaned 

 out in the seasons of 1872 and 1873) has been published in the Proceed- 

 ings of the California Academy of Sciences, from which the subjoined 

 section and topographical sketch have been reproduced. 



This cave is sitviated under a large isolated mass of porphyrite, which 



stands up like a low tower on a flat, 

 composed of old shingle-beaches, raised 

 a few feet above the present sea-level. 

 This flat unites higher areas of Amaknak 

 Island to the north and south. The 

 Cave Rock stands close to the beach, 

 and is probably a portion of an old reef, 

 an obstruction to which is probably due 

 >^ the formation of the flat. The rock is 

 about twenty-five feet high from the 

 level of the flat to its summit. Its sides 

 are abrupt, and it is covered with grass 



^^^^. 



AU 



Reduced cliart of the locality of tbo cave, sbo^inglhe 

 low isthmus between tlie higher porlions of the ialaud 

 north and south. 



Vertical 

 northeast of 

 stratum of " 

 Ijono layer). 



section of the Aniiikuak ( t\* shuwin^ Uh iulL the btach suuthweat of it, and the Hat isthmus formation 

 it. A, upper stratum of blown mold, mo^t modern diposit B, layer of shinple or beach-worn stones. C, 

 kitchen refuse", shells, &c. (Mammalian layer). D, lower stratum of organic mold with skeletons (Fiah- 



iibove. The neatest height of the cave inside is perhaps ten feet. The 



