85 



The material on which they grow can scarcely be spoken of 

 as soil. It is very dry, fairly hard and compact, composed of 

 mixed coarse and fine cinders, clinkers, ashes and charcoal 

 with a little clayey soil in a few places. 



The trees grow most plentifully on the higher and drier parts, 

 there being few or none in the occasional shallow depressions 

 where there is more soil and some stagnant water. These low 

 areas are occupied by grasses, weeds and young willows. A 

 broad, shallow stream of polluted water meanders across the 

 field. The birches stand well back from this stream. 



Some reasonably precise measurements gave the following 

 results : — 



The average height of the trees is twenty-four and a half inches. 

 The tallest was forty inches and the smallest was four inches. 

 The average thickness of the stems six inches above the ground 

 was a little over one fourth of an inch. On several plots fifty 

 feet square the number of trees averaged thirty-five. The total 

 number of young birches over the entire field of about ten 

 acres is about one thousand. 



The tallest trees in the stand are five years old, which means 

 that the earliest seeds took root on the plot the same season 

 the filling in of the swamp was completed. 



Interspersed irregularly among the birches are numerous small 

 willows averaging twenty-seven inches in height. There are 

 also many small locusts, some small-toothed aspens, poplars, 

 bay-berry, etc., all very young growth. There is much clover, 

 particularly in the hollows, and a great variety of weeds and a 

 few typical marsh grasses. 



No white birch trees grow anywhere in sight of this field but 

 a small group of mature trees was found about half a mile to 

 the north. There were about thirty-five of these trees, all well 

 formed, healthy specimens about twenty feet in height. These 

 trees might easily have supplied the seeds which gave rise to 

 the young growth to the south as there is practically no ob- 

 struction between them. 



Another more scattered stand of older white birches was 

 found still farther to the north and west in Van Cortlandt Park. 

 These trees are more numerous and larger than those already noted . 

 They are growing on the north and north-west sides of a long 

 wooded knoll interspersed w^ith stalwart oaks, tall beeches, 

 scrawny sumach and a few elms and maples. Their white 



