31-i Annals of the Carnegie Museum. 



graphic origin, but, as will be pointed out later, the more northern 

 portion is characterized by different plant-formations from those of 

 the southern portion. The northern portion of the sand-plain has a 

 soil coarser in texture, with a greater exposure to stronger air-currents, 

 thus constituting a habitat with a more unstable soil and more 

 xerophytic ecological conditions. 



There is no distinct line of demarcation between the drift-beach and 

 the sand-plain, tlie one shading off gradually into the other, the 

 theoretical limit of the drift-beach being, however, the extreme limit 

 of waves during winter storms. As the beach grows outward it is be- 

 ing continually built up in the rear, burying the driftwood more or 

 less completely and eventually attaining a height beyond the reach of 

 the waves. Much of the sand-plain is very little higher than the drift- 

 beach and in places the drift-beach appears to have been covered and 

 again exposed by the drifting away of the sand. Such areas of beach 

 again exposed, after having been once buried by the sand, have been 

 termed "fossil beaches," ^^ but, as they present at Presque Isle eco- 

 logical conditions practically no different than those obtaining in many 

 parts of the sand-plain proper, they will be considered as component 

 parts of the sand-plain habitat. 



Areas practically synonymous with the sand-plain, as herein recog- 

 nized, have been variously denominated as the ^^ back strand,'" Mac- 

 Millan ; " the ' ' upper beach, ' ' Cowles ; *^ the ''grass plain, ' ' Ganong ;^® 

 and in a more general sense have been included in the area of the 

 " dunes,' ^ Schimper ; ^' or '' middle dunes,'" Kearney.** The North 

 Haven Sand-plains as described by Britten,*' are in part also typical 

 of the sand-plain as herein described. Gleason's " blowout associa- 

 tion ' ' habitat ^^ of the Illinois River Valley sand region is almost an 



« Cowles, H. C. /. c. Bot. Gaz., 27 : 173-175, March, 1899; Whitfoid, H. N. 

 "The Genetic Development of the Forests of Northern Michigan." Bot. Gaz., 31 : 

 297-298, May, 1 901. 



■i^MacMillan, Conway. /. c., pp. 973-987. 



** Cowles, H. C. /. c. Bot. Gaz., 27 : 167-173, March, 1899. 



^® Ganong, W. F. /. c, pp. 88-94. 



*'Schimper, A. F. W. /. c, pp. 654-655. 



*« Kearney, T. H. /. c. Contrib. U. S. Nat. Herb., 5 : 367-395. 



■''•'Britten, W. E. <' Vegetation of the North Haven Sand-Plains." Bull. Tor- 

 rey Bot. Club, 30: 571-620, November, 1903. 



^"Gleason, H. A. "A Botanical Survey of the Illinois River Valley Sand Re- 

 gion." Bull. III. St. Lab. Nat. Hist., 7 : 1 49- 194, January, 1 907. 



