26 THE VICTORIAN NATURALIST. [Vol. XXIV. 



south-east of the Dolodrook junction. The rocks of special 

 interest in this area can be conveniently divided for the present 

 into the following groups : — 



1. Serpentine belt — Monument Gap and Dolodrook River. 



2. Black indurated slates of jasperoid character, with numerous 

 quartz veins — Dolodrook River, above Black Soil Gully. 



3. Black graptolite slates. Upper Ordovician — Wellington- 

 Dolodrook junction, &c. 



4. Bluish-grey crystalline limestone. Upper Silurian — Dolo- 

 drook valley. 



5. Yellowish-brown sandstones and mudstones of Wellington 

 spur. 



This separation is only made for convenience, and it is not 

 intended to convey the impression that all these divisions indicate 

 as many different chronological horizons. The only thing that 

 can be stated definitely just nov^' is that two distinct periods are 

 represented — the Upper Ordovician and the Upper Silurian 

 (Yeringian). The introduction of this second division is rendered 

 necessary by the occurence of the limestone resting as isolated 

 patches on the black slates. Fossils were recognized in a small 

 specimen of limestone shown to me by Mr. J. Macfarlane, who 

 went to some trouble to show us where this material occurred. 

 Several small occurrences were noted about half a mile south of 

 the Dolodrook River, from where the chromite occurs in the 

 serpentine. The limestone rests apparently on and is surrounded 

 by the graptolite slates. Mr. F. Chapman, A.L.S., has kindly 

 examined the fossils of the limestone, and his notes on these are 

 appended. 



Further notes on the rocks of the Lower Palaeozoic region are 

 postponed for the present, pending the microscopic examination 

 of some of the rocks. 



Some preliminary features in connection with the occurrence 

 of the igneous rocks of the Upper Palaeozoic series can now be 

 dealt with. In some respects these rocks form some of the most 

 interesting ones of the district. Their great extent and thickness 

 cause them to have a dominating influence over much of the 

 scenery of the Wellington and Moroka region ; their striking 

 banded or flow structure ; their variety in hardness, colour, and 

 texture ; their striking columnar structure in some sections, and 

 their interbedded relation to the sedimentary rocks all combine 

 to make them an interesting series. These rocks can be broadly 

 divided in the field into two readily distinguished groups : — 



1. Acid lavas, consisting of many varieties of porphyritic and 

 felsitic rocks. 



2. Basic lavas (melaphyres of Howiit). 



The first class is by far the most important. They comprise 

 those rocks referred to by Howitt and Murray as porphyries, 



