Vegetation of Northern Cape Breton. 



327 



luxuriant growth of lithophytic lichens, vegetation is scantily 

 developed. Common lichens on the shingle are Rhisocarpon 

 geographiciim (crustose), a form which is very conspicuous by 

 reason of its bright, greenish yellow color, and Lecidca tenc- 

 brosa Flot. (crustose) and Gyrophora kyperborea (foliose), both 

 of which are blackish in color. As a rule, however, even in such 

 places, there is more or less gravel and coarse sand underneath 

 the stony surface layer, while in the older parts of the upper 

 beach the shingle in some cases (Fig. 28) has been covered over 







Figure 28. — Spit near mouth of Barrasois River; to right, a typical 

 shingle beach; to left, a mixture of sand and shingle, overgrown with 

 Ammophila, white spruce, etc. 



by sand to such an extent as to produce conditions approximat- 

 ing those to be described presently as characteristic of sandy 

 beaches. All intergradations may be found on lea slopes between 

 rocky shingle at one extreme and sandy beach at the other. 



On the upper beach, soil conditions usually favor the develop- 

 ment of vegetation, and there may be a succession of plant 

 associations leading to the formation of a scrubby forest. The 

 pioneer plants here are predominantly herbaceous, and various 

 introduced weeds figure prominently. Indeed, almost no other 

 natural habitat supports a greater variety of weeds than shingle 

 beaches. In this connection it may perhaps be remarked that 



