84 



gi.test degree, except at one place, where a binary 



two 

 (lykef 



dykes 

 is of 



of diorite, 

 the usual 



intrusions do not appear to have metamorphosed the granitic 



rocks in the slii 



granite was found enclosed between 



whereas the granite exterior to the 



composition. 



Less frequent of occurrence and not largely developed, there 

 were found the following varieties of eruptive rooks : - - 



Diabase, intersecting granite and diorite. 



Eurite, as ill-detined intrusions in granite. 



Syenite is fairly developed in Skirmish Hill and Mount 

 Squires ; it forms a transition between porphyritic syenite and 

 typical syenite. The outline of the hills of syenite is less bizarre 

 than that of the granite hills. The glens and valleys among 

 them have every appearance of tectonic, and not erosive origin. 

 The syenite, as also the granite, carries sometimes veins of epi- 

 dote and epidote-rock (epidosite). 



Porphyrites in several varieties occur at Skirmish Hill. 



2. Volcanic Rocks. — A dark aphanitic rock, forming the top 

 of Mount Squires, may be referred to under this head ; it seems 

 to have penetrated the diorite. It resembles closely Tachylite, 

 though I hesitate to name as such, not liaving examined it 

 microscopically. 



3. TUFPAOEOUS Rocks — Surrounding Skirmish Hill, porphy. 

 ritic tufFas were found alternately with porphyritic breccias and 

 claystones ; they resemble closely a claystone (porphyrtuff) 

 occurring at Rochlitz, in Saxony, which carries also small veins 

 of lithomarge as a secondary product of decomposition, as does 

 also the claystone in question. 



4. ExTEA-LiMiTAL VoLCANic RocKS. — Two specimens of the 

 well-known obsidian bombs, and of the usual shape were col- 

 lected, one at Birksgate Range and one near Mount Squires. 

 No clue could, however, be obtained as to the oiiginal site, or in 

 explanation of their wide-spead occurrence. 



III. -MIKKUAL-1'R08PECT.S. 



As the Everard, Tomkinson, Cavenagh, and Barrow Ranges 

 consist almost entirely of eruptive, generally granitic, rocks, it 

 may be readily understood that they do not warrant any pros- 

 pects for minerals. Moreover, the scarcity of water (whicli is 

 insufficient in quantity for gold-washing on a large scale) and the 

 almost certain absence of any kind of surface-indications of vcuns 

 or lode-formations in these mountains are most unfavourable cir- 

 cumstances. Furthermore, the extensive cover of sand and loam 

 which allows only the uppermost and steepest parts of the ranges 

 being seen, is in itself a great drawback to prospecting. 



The marquee-shaped hills forming the Paheozoic l)elt, which 



