RYDBERG: PHYTOGEOGRAPHICAL NOTES 461 
MOUNTAIN CREST FORMATION 
If the gravel field or rock field is situated on the sloping moun- 
tain side, either under a snowdrift or along the course of the 
drainage, in other words where the moisture is greater and where 
more humus has a chance to gather, we have our third formation, 
which I shall call in lack of a better word the 
MOUNTAIN SEEP FORMATION 
This was included by Clements in the mountain meadow. 
While the mountain seeps have many plants in common with the 
meadows, there are found others wholly characteristic of these 
seeps, as for instance certain species of the saxifrage family and 
several willows. Where the ground is less sloping and the humus 
has had chance to gather still more, there is found the 
ALPINE MEADOW FORMATION 
If the drainage is imperfect and the water becomes stagnant, 
the next formation occurs, the 
‘ ALPINE BOG FORMATION 
or if deeper, the 
ALPINE LAKE OR POND FORMATION 
To this can also be added special formations. There are certain 
plants that grow only in the crevices of exposed cliffs. Hence, the 
CLIFF FORMATION 
Another is found only below and around the melting snowdrilts, 
the 
SNOW-DRIFT FORMATION 
Of these the rock-slides and mountain crest formations are 
decidedly xerophytic; the cliff formation mostly mesophytic but 
often xerophytic, the meadow and mountain seep formations 
mesophytic or the latter usually hydrophytic; of course, the bog 
and lake formations are hydrophytic. 
1. ALPINE MOUNTAIN CRESTS 
I shall begin with this formation, as ic is perhaps the most 
characteristic of the alpine formations. The plants are nearly all 
