1 10 THE NAUTlLUb. 



camping-grounds, an occasional broken stone-implement, and a few 

 shell ornaments that have been over-looked by tbe white man in his 

 starch for curios or prehistoric relies. 



Several theories have been advanced by scientists and others in 

 regard to the origin and ape of these islands, but 1 can add very little 

 to these flights of the imagination. How often, if more than once, 

 all or some of them have been submerged and raised above the sea 

 level, or whether those of the group which are composed principally 

 of metamorphic rocks are the remains of the highest peaks of a range 

 of mouutains that once formed or ribbed the most western part of the 

 continent, it is quite impossible to say. 



San Nicolas Island, however, is of sand-stone formation, and con- 

 tains beds of marine fossils, the forms being similar to those now 

 living all along the coast of the mainland, and I think we are safe in 

 suggesting that this island was thrown up at or about the time the 

 general elevation of the coast line and adjacent mesa-lands took place. 



There are always some curious expectations associated in the 

 human mind with thoughts of the islands of the sea. To the con- 

 chologist these expectations are often greatly multiplied, and these 

 little isolated patches of land become intensely interesting, and espec- 

 ially so to the student of terrestrial mollusks, for the islands of the 

 sea the world over are noted for their richness in land shells. 



In this respect, our Californian islands are no exception to the gen- 

 eral rule. While the number of so-called species found upon them, 

 so far as we know them at present, is not very numerous, several 

 are peculiar to these islands and not found elsewhere, while their 

 coloring, varied through closely related forms, adds unusual interest 

 and makes them very desirable for study, especially by those who are 

 interested in problems of evolution. 



The origin of the land shells of these islands and of the west coast 

 generally has been the subject of speculation by various writers on 

 the distribution of animal life for some years. In their attempts to 

 account for the affinities and resemblances, in a few instances, between 

 our land shells and some forms found in Asia, they have bridged over 

 Bering Strait, or " Behring Straits," several times had hands of 

 snails, or perhaps single ones " in pairs," as Pat would express it, 

 cross this bridge into America, travel southward to Cape Horn, 

 establish colonies all along this long line of travel, and subsequently 

 spread eastward over the continent, and finally cross another imagin- 



