454 BOTANICAL GAZETTE [ JUNE 
the surface of the water, and the island thus formed being added to 
by the action of winds, waves and currents, soon builds itself inward 
at one end nearly or quite to the mainland, forming a spit, and shut- 
ting off more or less completely a shallow bay or lagoon, which may 
be of small or of large extent. After the barrier is raised in front, the 
inclosed body of water, sooner or later, is surely filled up, and becomes 
solid land. If the portion of the bay bottom cut off by the “spit” 
was already filled with sand reefs and bars, with deeper places between 
them, the process of filling is hastened, for the bars are rapidly added 
to under the protection of the outer barrier, until their tops are near 
enough to the surface of the water to get sufficient light to enable 
seeds of water-plants, which may germinate upon them, to make suc- 
cessful growth. Such plants, once established, become very important 
factors in hastening the deposit of sediment. The growth of plants 
undoubtedly is also fostered by the shelter which the spit gives, as in 
the quiet water behind it the sand and other sedimentary deposits are 
practically stationary, while in front of it there is constant shifting 
under wave and current action, so that plants are unable to gain a 
foothold, where conditions are otherwise favorable. 
Such a spit-formed inlet, under ordinary conditions and with no 
fluctuations in the level of the bay, in the course of no very great 
interval of time would become partly filled with a series of islands, 
more or less sandy, and this phase would give place in due time to a 
marsh, in which would be strips of sandy or gravelly soil. In the 
meantime the spit would extend itself in breadth and length, and 
would form a new boundary for the waters of the bay, upon which the 
wind would heap sand and débris until a dune-line was formed. 
Actually one can read this story over and over again in the region 
under consideration, its variations being practically limitless and its 
editions of all sizes. 
There are easily found, also, evidences of periods of subsidence of 
the waters of the bay, of greater or less extent and duration. The 
past ten or twelve years have witnessed such a period, during which 
the water-level fell four feet, and even now, when the water is rising 
again, it is easy to see that the bay will never again occupy all the 
ground it did before its subsidence, for in bodies of water so shallow 
as Saginaw bay, a change of level of even a foot makes a very marked 
change in the shore-line, and competition for place is so keen among 
plants that every available inch of ground exposed by such a change 
it pr sre Lagoa iat 
