36 ECOLOGICAL RELATIONS OF THE FLORA. 



5. Dune Forest Formation. 

 Jack Pine Association. 

 Pine-Oak Association. 



Summary of Ecological Relations. 



Fungus Formations. 

 Phytogeographical Relations. 

 General Summary. 

 Literature Cited. 



PHYSIOGRAPHIC CONDITIONS. 



Sand Point is situated on the northern shore of Huron Count}', Mich- 

 igan. (Map.) As its name implies it is a sandy projection about 

 four miles long and from one-fourth of a mile to a mile vn.de, and ex- 

 tends almost directly westward into Saginaw Bay. The manner of 

 its formation has been discussed by Ruthven. In general it may 

 be said that it is composed of a series of more or less parallel ridges 

 formed by the elevation of sand beaches through wave and wind 

 action. Between the ridges are ponds, swamps, or low sand-flats, 

 depending on the depth. 



The beaches are of two types — the sand beach and the mud-flat. The 

 stretch of beach on the north side of the Point has a broad upper beach 

 and is built up entirely of sand. On the south side the point faces a 

 muddy, sheltered bay, Wild Fowl Bay, in which drift-wood and organic 

 matter are tending to change the sandy shore into a mucky one. 



On Sand Point, there are but two ponds of any size. Long Lake and 

 Orr Lake. These are lagoons that have been closed in by ridges formed 

 as barrier beaches or sand spits and elevated by wind action. These 

 lakes will never be reclaimed by the bay, as the water of the latter has 

 subsided since the}" have been formed and the separating ridges have 

 been well developed, and since the processes of filling will soon elevate 

 the lakes themselves to base level. 



In general then it ma}' be said that the Point has been and is 

 being constructed by the successive adcUtion of beaches that enclose 

 ponds or low flats. These beaches are subsequently elevated into 

 dunes, the ponds or lowlands gradually becoming converted into dry 

 land. The succession of habitats is therefore as follows: 



Mud-flat. 



1. Lake with the formation of a series of sand bars becomes 



2. Bay. A barrier beach or sand spit changes this into 



3. Lagoon or Closed Swale. Vegetation and inwash (and wind- 



blown sand if near the bay) changes this into 



4. Undrained Swamp or Marsh. Drainage and humus formation 



changes this to 



