CHAPTER II. 



ROCK CONSTITUENTS OF THE RUN. 



THE materials of which the station is formed are marl or " papa," sand- 

 stone, sandy marl, limestone, and conglomerate. Except the last, they 

 are obviously of marine origin. Marl is the foundation on which the 

 others lie, it is the bed-rock of Tutira. Whatever may have been its 

 origin, the remains of an ancient southern continent or not, its con- 

 stituents seem to have been carried by ocean currents or tidal action. 

 Deposition has been, at any rate, intermittent, not constant. Undulatory 

 lines of sand-grit can be traced on cliffs where flaking is constant and 

 where consequently exposures are clean. 1 Although so faint as to be 

 only decipherable in certain lights, like patterns in watered silk, they 

 nevertheless mark brief periods of quiescence as surely as the grosser 

 pelagic accumulations outcropping elsewhere on the run. The im- 

 mensity of these deluges of mud can be gauged by sand lines sometimes 

 yards apart. Their close recurrence can be inferred by interpolations 

 of sand so thin as to be practically invisible. 



The marls of Tutira vary in fertility and mode of weathering, the 

 least fertile being the most homogeneous and compact, the most fertile 

 those that disintegrate in cubes or exfoliate in peelings. 2 



We can now consider rock formations superposed on this base of 

 marl. To do so it will be convenient that in imagination the reader 

 should as before take his stand on the Maungaharuru range and again 

 traverse the run from west to east. 



The great dry bastion on the west is built up of alternate layers 



1 Such lines are particularly noticeable on the beach cliffs between Waikari and Mohaka. 



2 Through the kindness of Dr Lauder, of the Edinburgh and East of Scotland College of 

 Agriculture, a station sample of marl has been analysed. It "contained 34 per cent of calcium 

 carbonate (chalk), fairly large quantities of the oxides of iron and aluminium ; smaller 

 quantities of calcium and magnesium oxides. Phosphates were present, but no potash." 



