PIONEER PLANTS 
137 
The sand heaps, as has been stated already, represent for the 
most part the last of the material thrown np by the steam shovel, 
a coarse, gritty sand from the bottom of the ancient river bed. 
Due partly to the natural sterility of this material, partly to 
its inability to hold any amount of water, and partly also doubts 
less, to the fact that the lateness, of the completion of the heaps 
delayed the development of any vegetation they might have 
had, these artificial dunes did not present much in the way of 
plant life. A thin sprinkling of annuals, mostly Amarmnthiis 
retroflexus^ Chenopodium album, and Abuiilon theophrasti, to- 
gether with a few tufts of wild grasses, told the whole story. 
The shapeless western end of the embankment presents sev- 
eral interesting peculiarities in soil formation. The sand heaps 
opposite this part of the work are smaller than elsewhere, for 
the steam shovel dumped a good part of the sand from the bot- 
tom of the cut right on top of the soil from nearer the surface, 
instead of on the opposite bank. The result is that in places 
the top of the levee here is as sterile as the sand-heaps of the 
north bank, and the soil in general is sandier than it is on the 
levee proper. Even where the top is covered with sterile sand, 
however, the soil on the level space between the embankment 
and the channel is a sandy loam much like that of the levee 
proper, and it is on this table that most of the vegetation of 
this part of the area is concentrated. Here, and on the more 
fertile parts of the slopes, the vegetation is of the same general 
character as that of the eastern end of the levee, described be- 
low, while on the sandier parts it is more like that of the sand 
heaps of the opposite bank, though perhaps a little denser. One 
or two species were found here that were not found elsewhere : 
the Cynodon dactylon, and most of the Eragrostis megastachya. 
But it was on what I have already mentioned several times 
as the eastern end of the levee that the weeds flourished in all 
their' glory. Here the better soil from near the surface of the 
cut had been piled up and shaped into the real prism of the 
levee, and the sterile sand had been dumped out of the way on 
the far shore. In consequence the seeds that alighted here fell 
upon good ground, with only a few sterile streaks, and the tree- 
stumps and root-scraps of perennial plants had a chance here 
to take up anew the struggle fot existence. Moreover, this por- 
tion had been completed before the less favorable western end, 
and of course the plants here had a couple of weeks ’ start. And 
