THE MOLLUSKS OF THE PRIBILOF ISLANDS. 545 



From the limestone and argillite marine fossils have been obtained by Wossnessenski, Elliott, Dall, 

 W. Palmer, and C. H. Townsend, of which a collection exists in the National Museum, enumerated in 

 the following table. About twenty-eight species are known from this locality, which is stated to be 

 the only spot in the whole group where auy fossiliferous rocks occur,' the remainder of the islands 

 being composed of volcanic rocks and alluvium of very recent origin. 



Observations made in 1891 by Mr. J. Stanley-Brown,- special agent of the Treasury Department, 

 convinced him that at present no distinct trace of any limy stratum is perceptible in the Black Bluff. 

 The fossils obtained by him were contained in rounded, apparently water-worn, pebbles, which were 

 indiscriminately included in a general mass of volcanic ashes and other eruptive matter of which 

 the bluft" is formed. No extinct species appeared in the collection brought back by Mr. Stanley- 

 Brown, while several are noted from the material of the earlier collections. It would seem possible 

 that pebbles of more than one geological epoch may be included in the mass, or that the wear of the 

 waves for half a century has cut away enough of the bluff to hide or destroy the limy stratum 

 referred to by Grewingk and which may have been of limited extent. It is certain that from an 

 examination solely of the material collected in 1891 the fossils might be referred to an age as late as 

 the post-Pliocene, which would not agree very well with the fauna reported by Grewingk and others. 

 The fossils collected by Mr. Stanley-Brown and not included in the earlier collections are as follows: 

 Bucciniim tenue Gray?, B. polare Gray?, Admeie couthouyi Jay?, Leda sp., Yoldia Umatula Say, 

 Pseudojiythina grandia Dall, Carditcm islandicum (very abundant), Macoma sabulosa Spengler, and a 

 fragment possibly of a Panopea. All these occur lying at moderate depths in Bering Sea, adjacent 

 to the island, at present. 



This deposit has been discussed by Dr. George M. Dawson,'* -vyho corroborates Mr. Stanley. 

 Brown's description of the conditions under which the fossils are found, but regards them as having 

 been detached from the sea bottom by a volcanic eruption, with the products of which they were 

 mixed, and therefore does not consider them as fixing the age of the formation in which they occur, 

 but only as representing beds already in existence at the time of the eruption. 



COMMANDER ISLANDS. 



On the Commander Islands, west of the Aleutians, rocks of the same age probably occur, since 

 on Bering Island Stejneger collected some specimeps of a conglomerated hard gravel of highly 

 polished pebbles united by a limy cement, containing fragments of bivalves (Saxicava?) and a single 

 piece of claystone with the imprint of a bivalve not yet identified. 



' Cf. H. W. Elliott, Condition of Affairs in Alaska, 1875, p. 70. 



2 Bull. Geol. Soc. Am., Ill, 1892, p. 496. 



3 Bull. Geol. Soc. Am., Vol. V, 1895, pp. 130-132. 



5947— PT 3 35 



