200 NINETEENTH REPORT. 



this formation will not be referred to again, a description of its vegeta- 

 tion will be given at this point. 



The sand ridges have a characteristic cover of Quercus rubra, Quercus 

 velutina, Pinus Banksiana, Pinus Strobus, Pinus resinosa, with Vaccinium, 

 Gaylussacia, Epigaea, and Gaultheria undergrowth. The depressions 

 show all phases of hydrarch successions, from Nymphaea up, including 

 sphagnum bogs with Sarracenia and Betula pumila, and Chamaedaphne 

 meadows with Vaccinium corymbosum and similar forms. Along the 

 Michigan shore runs a narrow belt of low shore dunes, more or less 

 rejuvenated. In appearance and vegetation they are similar to those 

 around Point Betsie, to be described later. 



Another relic of Nipissing times is an elevated beach just north of 

 the lighthouse at Point Betsie. (Plate VI, Fig. 1.) The reason for 

 its preservation is probably its proximity to glacial gravels which formed 

 a protecting layer of shingle so that now the beach looks very much 

 like a railway embankment, preserving its original sloping front toward 

 the water, with a similar slope on the opposite side, caused by the wind 

 blowing out the sand from among the pebbles. 



3. Dune formation. Soon after the recession of post-glacial lakes 

 the wind began its work of piling up dunes. Apparently tliey were at 

 first located much farther west, on land since eroded by the lake. They 

 have been continually in motion, passing through the usual cycles of 

 fixation and rejuvenescence. They are found in two main localities in 

 this region. A large complex on the Crystal Lake Bar surrounding the 

 present Point Betsie, and a small group of perched dunes, called locally 

 from their chief spectacular feature, the "crater" group. 



a. Point Betsie Complex. (Plate VII.) This group is located on 

 Crystal Lake Bar, starting in a point on Lake Michigan at the western 

 end of the grounds of the Congregational Summer Assembly, and spread- 

 ing like a fan toward the north, and is about two miles in length and 

 lialf a mile in width at its widest point. Its elevation varies from the 

 water level to ridges upwards of 200 feet in height. At the southern 

 extremity of the group the dunes are fixed, and extend from bluffs on 

 the eroding shore to a steep lee slope on the eastern side. The contour 

 is very uneven, showing dune ridges and outlines of blowouts. These 

 are covered by a climax forest and have evidently been untouched for 

 a very long time. Approaching Point Betsie the shore cliffs gradually 

 become lower, and give place to a complex of moving sand. Great 

 troughs lead from the shore for half a mile or more inward, to the 

 advancing lobes of the lee front. Among these blowouts are found 

 residual patches of the original forests. Just north of Point Betsie is a 

 rather large patch of relic forest on three dune ridges, which extend 



