Vul. XXVI 1 1. 



] Excursion to Sydenham, Bulla, and Diggers Rest. 5 i 



EXCURSION TO SYDENHAM, BULLA, AND DIGGERS 



REST. 



Fourteen members of the Club and half-a-dozen geological 

 students from the Continuation School caught the 6.42 a.m. 

 train for Sydenham on Monday, the 24th April (Eight Hours 

 Day), to take part in a geological trip in the neighbourhood of 

 Bulla. The party was increased in number at Bulla by three 

 other members, one of whom had missed the early train and 

 had walked out from Essendon, while the other two had 

 motored out from Brighton. The features examined during 

 the day are to be found on Quarter Sheet No. 7, S.E., of the 

 Geological Survey of Victoria, and some notes as to the geo- 

 graphy of the district will be found in the report of an excursion 

 made by the Club some years ago {Vict. NaL, vol. xvii., p. 120). 



From Sydenham railway station we walked across to the 

 Saltwater River, taking a course north-westerly along the 

 railway line at first for about a mile, and then almost north 

 across the paddocks for another mile and a half. We first 

 noticed the deeply-sunk valley of the Saltwater River, about 

 230 feet below the level of the basalt plain. On the out- 

 pouring of the basalt sheets the pre-basaltic drainage system 

 was obliterated. The new rivers wandered about on the fairly 

 level basalt plains as they made their way to the sea. This 

 meanderine course, once attained, was to a great extent per- 

 sisted in, the rivers gradually trenching their channels deeper 

 and deeper, until now they flow in a sinuous course at the 

 bottom of very young valleys, which they are still actively 

 corrading as well as laterally eroding. The basalt of the plains 

 near here is very vesicular, one vesicle we measured being over 

 15 inches in length. About 400 yards west of the famous 

 " Organ Pipes," which have been so admirably described by Dr. 

 T. S. Hall in the excursion report previously mentioned, were 

 to be seen the tops of partly denuded basaltic columns, showing, 

 by the angles they made with the horizontal, that just at this 

 locality a pre-basaltic river channel must once have existed. 

 The sides of this ancient river-channel were mantled with 

 argillaceous sand overlying shales, probably Ordovician in 

 age, having a general northerly strike and a high angle of dip. 

 After viewing the " Organ Pipes," a mass of basalt columns 

 forming a river-cliff on a concave bend of the Saltwater River, 

 we climbed out of the valley and passed over the basalt plain 

 to the north-east for a distance of slightly less than two miles. 

 Here we met with the entrenched meander on Deep Creek 

 figured in Professor Gregory's " Geography of Victoria," on 

 p. 152. This feature is about a mile and a half south of Bulla. 

 Usually, entrenched meanders are due to the revivification of a 

 stream causing a new young channel to be cut down in the 



