780 EMEBY [chap. 28 



SO carried were highly prized by the natives, frequently being designated as 

 belonging to the chiefs. Occasional loose exotic stones found on the beaches of 

 coral islands by Chamisso (1821) and by many later travellers j^robably arrived 

 via driftwood which afterward decomposed. Although the quantity of rocks 

 transported by driftwood is small, both the size of individual rocks and the dis- 

 tances are great. 



Distance from shore is much less limited for rafting by driftwood than by 

 kelp, so one might suppose that rocks carried by driftwood might be distributed 

 thinly but widely throughout the oceans. There may be some relationship to 

 major rivers and forested regions. Probably most of the rocks so carried are 

 angular and many are weathered. 



Erratic rocks are common in ancient sedimentary strata, particularly in 

 coals, of Britain, Europe, Australia and the United States (Emery, 1955). 

 Most likely these rocks were held by tree roots and rafted to the sites of their 

 burial in coastal swamps while others were carried to the ocean beyond. 



4. Sea Mammals 



Gastroliths have been found in most of the smaller sea mammals — sea-lions, 

 sea-elephants, fur seals, harbor seals and walrus (Hamilton, 1934; Scheffer, 

 1950; Fleming, 1951, 1953; Brooks, 1954; Loughrey, 1959; see other references 

 in Emery, 1941). Most gastroliths consist of stones which are slightly to well 

 rounded. Occasional mollusk shells, usually beach w^orn, are also present; 

 Andree (1920, p. 393) reported more than 500 shells of Mya truncata in the 

 stomach of a single walrus. Individual stones have been recorded with diam- 

 eters up to 10 cm and weights to 2 kg, but single stomachs have contained 

 more than a hundred individual stones. The largest aggregate weight reported 

 is 37 kg in a sea-lion (Mohr, 1952), but weights of more than 5 kg are unusual. 

 There is no agreement as to why stones are picked up and carried as gastroliths ; 

 the animals may use the stones as an aid in triturating their food, as ballast, to 

 destroy nematode worms, or perhaps they merely pick them up in play. In any 

 event stones have been found in males and females, in old and young, even in 

 milk-feeding pups, and in all seasons. Where stones are lacking, other objects 

 may be picked up. For example, a harbor seal in an open tank at the Steinhart 

 Aquarium in San Francisco became a floating bank; according to E. S. Herald, 

 Curator {in litt.), "it had swallowed $7.48 in coins, ranging from French 

 centimes to U.S. 500 pieces. Corrosion of copper pennies indicated that some of 

 the coins had been in the stomach for a considerable length of time. Eventually, 

 of course, this resulted in the demise of the harbor seal. " 



More is known of gastroliths in stomachs of the California sea-lion {Zalophus 

 californianus) than of other sea mammals, owing to collections made by A. L. 

 Kelly (Scripps Institution of Oceanography) and Emery along the mainland 

 and islands of southern California and Mexico. Stones were found in 73 of 170 

 stomachs (Fig. 3). Where land geology is well known and the local rocks are of 

 diagnostic types, it is possible to determine whether or not the sea-lions picked 



