304- Postelsia 
Plate XXI. «1. Small depressions im sand- 
stone near high water line. 
2. Regions of young pools. 
Plate XXII. 1. and 2. Irregularities. in jouter 
shore line arising from wearing out of tide- 
pools. 
Plate XXIII. 1. Irregular pools formed by 
union of several small pools. 
2. Series of pools reaching above 
ordinary high water. 
Plate XXIV. Tide rift formed from several 
pools. 
Plate XXV. 1. Tide-pools in various stages 
of development. 
2. Tide-pools formed in shale. 
