46 GEOLOGICAL EXCURSION TO PORT CYGNET. 



These intrusive rooks carry pyrites, and along the lines of 

 their contact with the Permo-Cai'b(jniferous sedimentary 

 strata some silicification has taken phice, accompanied by a 

 concentration of pyrite. Some of the contact stone assays 

 5 to 6 ozs. silver and from fdwt. to 2 or 3 dwts. gold per 

 ton. The district has yielded about 3000 ozs. alluvial gold, 

 most of which was derived from the small flats near 

 Lymington. 



The variations which distinguish the Port Cygnet rocks 

 from alkali rocks elsewhere may be appealed to in illus- 

 tration of the theory of petrological provinces. They 

 cannot be exactly correlated with the known members of the 

 series elsewhere, and possibly new names may be required 

 for some of them. 



The study of the group is not complete, and as it pro- 

 gresses readjustment of the nomenclature are inevitable, but 

 at present the series would be arranged as follows : — 



ALKALI ROCKS. 



Family 1.— Alkali Granite. 

 Not represented. 



Family 2. — Alkali Syenite. 



{a) Plutonic representatives : — 



1. Quartz augite syenite : a medium-grained, yellowish 



rock at Regatta Point (alkali felspar + augite + 

 quartz). 



2. Alkali syenite at Regatta Point and on Back Road 



(orthoclase and albitic felspar + augite + amphibole 

 with accessory biotit^, quartz, sphene, and apatite). 

 Has frequently a porphyritic facies. 



Family 3. Elaeolite Syenite. . 



(a) Plutonic representatives : — 



1. Elaeolite syenite : coarse syenite rock at Regatta Point, 

 and near top of Mount Mary (alkali felspar + elaeo- 

 lite -f- alkaline pyroxene + amphibole). Contains 

 melanite and biotite, also hydronephelite after elaeolite 

 [or sodalite], and accessory sphene and apatite. 



(b) Complementary and dyke representatives : — 



1. Elaeolite Syenite porphyry, viz - 



(i.) The biscuit felspar rock on Mount Livingstone 

 and Mount Mary ("Magpie") [orthoclase 

 and a little triclinic f('ls])ar -\- alkaline 

 pyroxene and am])liibole + melanite and iron 

 ore pseu(lomori)hs after nosean and garnet 

 with natrolitic pseudomorphs after nepheline 

 (or sodalite)]. Has a fluidal felspathic 

 ground mass. 



