144 



Tlie prevailing strike about Wangaraleednie is a few degrees 

 west of south to a few degrees east of north, but changing in 

 the northern part of the area to S. 20° E. and N. 20° ^Y. The 

 beds have an easterly dip at very high angles and show much 

 local contortion. The following minerals were collected from 

 the granite dykes : — Albite, orthoclase, muscovite, hornblende, 

 chlorite, quartz, garnet, galena, and calcite. ^ A compact mag- 

 nesite occurs in veins in a talcose state in the Oolabidnie 

 Creek. 



Geological Sections about Welliis'gtox oe Noeth-east 

 Shoee of Lake Alexandeina, by Professor Ealph Tate. 



Section Point Pomond, Lake Alexandrina. 



II. South-west Pace. 



The section is princi- 

 pally occupied by gypsum 

 in the form of slightly 

 coherent grains, or com- 

 pacted into a tough rock, 

 showing much false bed- 

 ding, and at some points 

 fills the whole section 

 below bed No. 2. 



A bluff on the east side 

 of the lake is similarly 

 composed of small incohe- 

 Estimated total ....32 6 rent particles of gypsum. 



The false-bedded arrangement of the gypsum indicates that 

 the original material of the stratum was not tranquilly de- 

 posited — possibly in shallow waters of a lagoon or lake — a 

 view corroborated by the fact of the horizontal replacement of 

 clays by it. Whether the gypsum was accumulated as we now 

 see it, or whether it is pseudomorphic after a calcareous sand, 

 I can offer no definite opinion. The condition of the particles 

 of the gypsum-sand rock, though granular, shows in a great 

 measure' a tendency to a crystallised form; and on the other 

 hand, the more compact portions, which show a well-developed 

 crystalline structure, have included grains of a white or ^ red 

 marl. An impure band underlying the gypsum bed is a 

 mass of granuhxr gypsum largely permeated by an ochreous 

 paste. An analysis of the gypsum-sand rock gave S'O per cent, 

 of free silica and aluminous residue, and a little iron oxide. 



