338 po s t e I s ia 



these together are masses of broken shale, chips 

 of myriad shells and other material incident to 

 shore line deposit. Such is the base of the 

 Miocene sandstone. Quite steadily the frag- 

 ments of shells and shale diminish in quantity 

 and the rock becomes a sandstone of the light 

 gray, medium grained, siliceous type, so common 

 everywhere as a shore-fringing sediment. Its 

 cementing material in the lowest layers is calcium 

 carl^onate whose origin is in the shell fragments 

 of the Tertiary shore. 



Within this sandstone are many variations of 

 texture and hardness. Walking over the planes 

 of gentle slope which dip beneath the waters of 

 the Strait of Fuca, the way is difficult because of 

 ridges and mounds which are of harder and more 

 unyielding rock. Between these the waves have 

 washed out the softer sand, plants have loosened 

 the sand grains by crowding between them their 

 root-like processes to search for mineral foods 

 and secure mechanical support. The alternating 

 harder and softer portions afford place for 

 varied work of the waves. The hard rock is 

 the projecting reef on which Posfehia and its 



