200 PROCEEDINGS OF THE AMERICAN ACADEMY. 



by the sea. Therefore the straight coasts of Jutland, Italy, etc., as given 

 on page 246, are the forms of the stage next succeeding that of the 

 vanishing island. 



Complex Cases of Tying. — Many of the actual examples of island- 

 tying are not simple. A great variety of combinations occur in nature, 

 but only three will be here considered, viz. where several tombolos unite 

 a group of islands, where rivers surround islands with their waste, and 

 where slight movements of the land have assisted tying. 



Samso Island is composed of two higher portions joined by a lower narrow neck 

 (Denm., SamsiJ). The central portion of this neck is lieath and forest, presumably 

 overgrown marsh, bounded on either side by gently curved shores. These curves 

 also indicate tying and complete filling, for the coast farther north and south has 

 not such smooth outlines, indicating that the present position of the land has not 

 been maintained for a time sufficiently long to develop such curving shorelines. 

 The left hand end of the eastern bar is complicated on account of numerous small 

 islands. 



Three islands in Lenox cove, Tierra del Fuego (II. O., 455'). 



West of Magdalena bay an island between cape Corso and Entrada point is tied 

 to another island at cape Lazaro (II. ()., G21, G44).* 



]Marambava mountain, 20GG feet liigli, has a twenty-mile tombolo extending to 

 the mainland of Brazil, which close to tlie sliore is broken by a tidal opening. A 

 spit from the tombolo inside of Sapetiba bay is growing toward Jaguanao island 

 (H. 0., 488). 



In Boston harbor there are three groups of islands tied by numerous tombolos 

 (C. S., 337; G. S., Boston, Boston Bay, Mass.), viz. the Winthrop, tlie Quincy, 

 and the Nantasket groups. Marshes occur in all three, indicating adolescent 

 development. 



Sidi bon Said (Tunis, A'll, VIII, XII, XIV, XX, XXI) is on an island which 

 is tied to tlie Tunis mainland by three bars. The central one is 5 to 8 kilometers 

 broad, 10 kilometers long, and has an elevation in places of 10 or 12 meters. 

 Whether this broad istlimus was originally two tombolos enclosing a lagoon, or was 

 made land by elevation, is not certain from map inspection. Later, however, two 

 tombolos have been built from eitiier end of the island, enclosing between them 

 and the earlier built isthmus two lagoons, Sebkhat er Riana and Lac de Tunis. 



Leucate (Fr., 255) is an island of Oligocene strata, tied by one tombolo to the 

 mainland, and has also a wing-like bar on both the right and left sides. These wing- 

 bars are built up from the bottom in large measure, according to the indications 

 given by the right-angled abutment of the left end of the right bar against Leucate, 

 and a similar abutment of the left bar against the older land near Port Vendres 

 (Fr., 258). Tlie stream deflections indicate alongshore motion to the right, which 

 is also suggested by the offset of the right wing-bar by the left. 



The island of Cette (Fr., 23.3) , of Jurassic strata, is tied by the wing-bar from the 

 left side of the Hhone delta. To the southwest the volcanic knob of Agde is more 



* In regard to dislocation as a probable cause of these islands, see W. Lindgren, 

 Proc. Cal. Acad. Sci., 1888-90, I. 173, II. 1, III. 26, and references there given. 



