212 G. L. COLLIE WISCONSIN SHORE OF LAKE SUPERIOR 



out them, though other conditions ma}'' favor their ])resence. The 

 existing spits on the islands are small, usually extending but a lew rods 

 into the lake. Formerly much more extensive spits occurred on the 

 islands, but they have disa[)peared gradually, until at the present time 

 no extensive deposits of this type are found, though shoal deposits ex- 

 tend out into the lake from the end of certain spits, and these shoals 

 indicate in some degree the former extent of the spits. 



TOMBOLOS 



This type of shore de])osit is found in a few instances. The best ex- 

 ample is found on Presque isle. In this particular case two islands, once 

 separated by a channel of water at least 2,000 feet wide, are connected 

 by a broad bar of sand and gravel. York island is another example of 

 the same phenomenon. Here two small rocky islands are connected b}'' 

 a bar of sand a hundred yards long. vSand island is tied to the main- 

 land by a bar of sand at least two miles long, which has not as yet ap- 

 peared above the water. The depth of the water over the bar is slight, 

 not exceeding seven feet— a good example of an incii)ient tombolo. 



BEACHES 



The various types. — Beach deposits are connnon l)oth on the mainland 

 and on the islands. Tliere are four recogniza})le types, namely, the 

 })latform, the barri(?r, the cliff, and the storm beach. 



riatfonn beach. — This type is found on Michigan and Madeline islands. 

 Its chief characteristics are a loo})cd ))ar or ridge of gravel and sand 

 formed on an old wave-cut platform, the whole ridge inclosing a lagoon 

 within. The Michigan Island occurixiuce is a good example of the type. 

 During the Madeline stage the lake cut a well defined bench and sea- 

 clilf. The cliflf itself is cut in glacial debris and reaches a height of 40 

 feet. It extends across the island and is extremely well defined. In 

 front of the cliff stands the bench, covering ])ossibly 800 acres. It is 

 triangular in form, with the base resting against the base of the cliff. 

 The bench stands several feet above the lake, as a whole, but there is a 

 gradual slope from the clifi' to the lake. Where the sloping bench meets 

 the lake the waves have thrown up a ridge of sand and gravel about 

 the i)erii)hery of the bench. Naturally this forms a looped bar, because 

 of the sha})e of the bench. This ridge is broad and low, slo})ing in front 

 toward the lake like an ordinary beach. Indeed, it has the character- 

 istics of the usual beach formation. Within the looped bar is a lagoon, 

 Avhich covers several acres, though it has become filled in large part 

 with debris. 



