ROCK CONSTITUENTS OF THE RUN 



11 



stones of the east show fresher and fuller signs of marine life. Their 

 sand is more truly sea sand. Their limestones contain a larger number 

 of shell-species closely connected, or actually identical with those now 

 existing in the pertingent seas. Above several of the limestone bands 

 are shallow deposits of a highly friable ferruginous matter. On the 

 cliffs of the east, too, there supervenes a new and most important factor. 

 In this region the marl bands interpolated at irregular intervals, rapidly 

 crumbling, sap and undermine the more durable strata ; the cliffs are 

 somewhat less sheer, the strata exposed having weathered less evenly. 

 From the sea-floors thus sapped great quadrilaterals rock cleavage 



Sea-floors on Eastern Tutira. 



is similar to that of the western limestones have already dropped out, 

 whilst others projecting into space also appear to be about to break 

 away. 



To recapitulate : The base of the whole station is blue marl rock 

 or "papa." Superposed on it rest the ranges of the west formed of 

 sandstone and limestone, the ranges of the centre formed of compressed 

 sandless pebble-rock and slaty sands, the ranges of the east built up 

 of layers of marl, sandstone, and limestone. 



Of these masses of material, the sandstones and conglomerates 

 extend over nine-tenths of the station and are of little value. Such 

 elements of fertility as exist are contained in limestone outcrops, in 

 masses of travertine, but especially in elevated streaks of marl. 



