176 BOULDER REVEKIES. 



hind feet would give a quick upward and down- 

 ward stroke. In this way he kept his perpen- 

 dicular position with head above water for sev- 

 eral minutes. 



Great boulders of granite, gneiss or other 

 form of igneous rock, moss covered and pitted 

 by the frosts of centuries, protrude from the 

 side of some steep bank or rest in the midst of 

 the stream itself, the space beneath their angled 

 sides furnishing a secure and shady retreat in 

 which the larger inhabitants of the pool find 

 refuge when danger threatens. If, perchance, 

 the boulder occupies the middle of the stream, 

 below it will be found a little delta or bar of 

 sand formed during freshets by the friction, 

 union and consequent slowing up of the two cur- 

 rents of water which were split above the boul- 

 der as the flood dashed along. These lifeless 

 boulders are older by many centuries than the 

 stream itself, and often form perches upon 

 which the sentinel frog rests, his hues blend- 

 ing with those of the mossy cover. Here, too, 

 the handsome lady turtle, or its larger cousin, 

 the snapping turtle, delight to lie and sun them- 



