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PROF. E. W. SKEATS ON THE GNEISSES [Aug. I9IO, 



III. Geological Relations in the Field. 



(a) Description of Geological Boundaries. 



The accompanying sketch-map (fig. 1) shows the geological 

 boundaries in the area described. The Dandenong Hills, composed 

 of dacite, lie for the most part to the north of the area, while on 



the south the grano- 

 diorite extends for 

 some miles beyond 

 the limits of the map. 

 The line of separation 

 between the dacite 

 and the granodiorite 

 runs approximately 

 from west to east, 

 generally occupies re- 

 latively low - lying 

 ground, and for a 

 considerable, distance 

 closely follows the 

 course of Monbulk 

 Creek. The narrow- 

 gauge railway from 

 Ferntree Gully to 

 Gembrook runs for 

 some distance almost 

 parallel to this boun- 

 dary, and some little 

 distance to the north 

 of it. Between Aura 

 and Emerald, how- 

 ever, the railway - 

 line crosses the boun- 

 dary between the two 

 rock series, and the 

 stations along this 

 line give the most 

 convenient access to 

 the area. The length 

 of junction examined 

 is about 6 or 7 miles. 

 At the western end 

 of the line, the junc- 

 tion of the two series 

 is obscured beneath the alluvium of the lower part of Monbulk 

 Creek. At the eastern end, near Emerald, the junction is hidden 

 beneath a later basaltic flow. 



