for the year 1864. lxxxv 



rable accuracy of their detail ; although the great additional 

 labour and delay has been thrown on the department of 

 making a great portion of the topographical map, and nearly 

 all the physical feature-shading required as a basis on which 

 to plot the proper geological work. 



During the last twelve months, the field geologists have 

 mapped an area of about four hundred square miles, a 

 great portion of which, being more or less auriferous country, 

 has required that the physical features should be minutely 

 laid down : these include gullies, quartz reefs, igneous dykes, 

 and the contouring of hills. This makes about 3,500 square 

 miles of the colony now geologically mapped. The staff 

 engaged in this work has consisted of three field geologists, 

 one assistant field geologist, and nine men. The districts in 

 which they have been at work during the past year are 

 Yandoit, Pentland Hills, Ballan, and the Campaspe, north 

 of Barfold. Besides this regular and progressive work, the 

 auriferous and argentiferous reefs of St. Arnaud have been 

 carefully examined, as well as the processes in use there for 

 treating the silver ores for the extraction of the silver, and 

 a detailed report on the same by one of the staff, Mr. Ulrich, 

 is nearly completed The quartz reefs at Wood's Point have 

 been also visited and reported on. 



Amongst the more interesting points of discovery by 

 the Survey during the year, is the occurrence of an 

 auriferous drift resting on basalt, and overlaid by a 

 subsequent flow of the same rock. This was met 

 with by Mr. Daintree, within little more than a mile of 

 Mr. Lyons' homestead, at Ballan. A painty of miners have 

 been tunnelling this lower basalt under Mr. Dain tree's direc- 

 tion, with a view to drain the water from the superincum- 

 bent drift, to enable them to work it more conveniently 

 and economically. This basalt rests on the Bacchus Marsh 

 sandstones, which again repose on lower silurian beds. Of 



