178 C. W. MARSH. GEOLOGICAL NOTES 



are for the most part absent, but when present, are usually 

 found to run continuous for long distances parallel with the other 

 rocks. The more hilly country, sucli as the Mount Gipps Ranges 

 on the north-east, the Waukaroo Ranges on the north, and the 

 Mundi Mundi Ranges on the north-west, are principally made up 

 of these rocks, in parts of which however, irregular out-lying 

 portions of the upper rocks occasionally appear. Whether these 

 two apparently dissimilar formations are stratagraphically con- 

 formable or otherwise, remains for future study to decide, while 

 if they graduate into each other by almost insensible transitions, 

 as in some instances they appear to do, the solution of the problem, 

 in the absence of fossils, will be no easy task. 



The most noticeable differences between these and the metalli- 

 ferous group of rocks above them are that the argillaceous and 

 calcareous members of the former appear to be represented by the 

 micaceous schists and hornblendic rocks of the latter, while the 

 extensive tracts of highly granitic gneisses in the lower are but 

 sparingly represented in the upper, where as a rule, the gneisses 

 are more decidedly schistose. The whole of these rocks, inclusive, 

 are more or less intersected by dykes of dolerite, often micaceous; 

 diabase, frequently porphyritic diorite, from aphanitic to coarsely 

 crystalline; a hornblendic rock, decomposing readily on exposure, 

 and not easily defined, and granite. These intrusive rocks are 

 often transverse to the strata and traceable for long distances, at 

 other times following the strike of their enclosing rocks. These 

 dykes, so far as observed, appear to be common alike to both 

 divisions, but if any should be found restricted to the lower and 

 absent from the upper rocks, they may greatly assist in fixing the 

 lines of demarcation. Besides these dykes, which have the appear- 

 ance of being decidedly intrusive, there are veins and irregular 

 masses, very similar to some of them in their more essential 

 mineral ingredients, which are often found passing over by slow 

 graduations into metallic veins and deposits. These irregular 

 deposits, which are usually limited, both in length and depth, and 

 seem generally to have no connection with extensive fissure open- 

 ings, will be more fully described in connection with ore-deposits. 



A systematic classification of these rocks would be very difficult 

 and require a large amount of patience and study, since, not only 

 do progressive changes take place at different horizons, but along 

 almost any continued extension of strata on the same horizon. 

 For instance, talcose schist imperceptibly changes into mica schist, 

 which by the presence and gradual increase of feldspar, passes 

 insensibly into gneissic-mica-schist, and finally into gneiss, whilst 

 the latter, by the loss of its mica, the development of garnets, or the 

 change of its schistose structure, passes respectively into binary 

 granite (aplite), granulite, and granite. Similar changes by the 



