THE WoKK OF ORGANISMS IN ROCKS. 5 



We may divide the work of organisms into two 

 classes, passive and active. 



In the former they are controlled by external 

 influences, and as the effects are not important I shall but 

 briefly refer to them. In their active capacity the work 

 accomplished is the direct result of the living forces with 

 which the}' are endowed 



In both cases it will be convenient to refer to the 

 results achieved under the heads just mentioned — 

 Disintegration, Transport, Accumulation, Protection, and 

 the changes brought about after Deposition. 



1. As Passive Agents. 



In the gorse-covered slopes at West Kirby we meet 

 wifh rocks channelled and grooved on their vertical faces. 

 The grooves are two or three inches wide and equally 

 deep. On a windy day the gorse growing near the rocks 

 sways with the wind, and by constant rubbing excavates 

 the groove. On soft, loose-textured rocks the wearing 

 takes place very rapidly. Probably the ordinary agents 

 of weathering would take hundreds of years to crumble 

 away the rock as much as the gorse does in a few seasons. 

 On sand dunes rootlets and grasses swept by the wind 

 may produce similar effects. Wind, too, may uproot 

 trees, which in falling break up the soil and stones 

 entangled in the roots. 



Moving water, in carrying sea weeds and loose 

 organisms over a stretch of sand or mud, scores and 

 excavates, leaving hollows to be filled in by the next tide 

 or by blown sand. These features are found in the fossil 

 condition, and were the subject of much controversy until 



