oyO PROCEEDINGS OF SECTION C. 



this lava there is a dense, dark, flinty looking stone a mile or two 

 to the west, which in microscopic slides presents a similar 

 appearance. 



Outside of the principal area of volcanic rocks another smaller 

 one extends from the Mooree Ford, on the Glenelg, to the township 

 of Chetwynd. At the first-mentioned locality there are two 

 smooth, roimded, conical hills, and at the latter a smaller and 

 more pointed one of a rugged character. All three consist of lava, 

 which, at least from the Chetwynd hill, flowed for a short distance. 

 In composition (judging from its appearance under the microscope) 

 it resembles the Adam and Eve rock. Tlie country is much broken 

 along the line of the formation, and the roads skirt it as far as 

 possible, keeping in the adjoining granite. 



At Koolomert Station, about halfway between the eastern and 

 western boundaries of the area, some remarkable rocks are exposed 

 in a quarry on the side of a hill. They are prismatic, and stand 

 in slender vertical columns, loosely cemented together. Some are 

 four and others five sided. 1 hey vary very much in thickness, 

 the smallest being about l^in. in diameter. With care, prisms 

 fully 2ft. long can be separated. In the quarry they are much 

 longer than this, but it is diflScult to avoid fracturing them when 

 using the necessary tools. Being light colored and gritty, I 

 regarded them at first as sandstone, rendered prismatic by igneous 

 agency. A better explanation can, however, be given. Higher up 

 the hill, and just above the quarry, a basic lava crops out, which, 

 at least in its deeper-seated portions, was evidelitly prismatic. 

 The prisms are still there, but the rock itself has been greatly 

 altered, and now looks like a sandstone. I am informed on good 

 authority that the same prismatic rock appears on the surface at 

 a short distance to the south of Chetwynd. 



Another rock mass has yet to be mentioned, situated a little to 

 the west of the main volcanic area, and separated from it by 

 granite and sedimentary (Mesozoic) strata. About five miles to 

 the north of Casterton, on the road to Chetwynd, the River Wando 

 passes through a gorge between tw^o hills, which are locally called 

 " The Hummocks." They consist of rocks of a vivid green color, 

 and somewhat fissile. Some specimens collected show an asbesti- 

 forni structure, and others might be called picrolite. In the mass 

 the rock is essentially serpentine, with magnetite grains disseminated 

 through it. A rough analysis made some years ago gave nearly 

 80 per cent, of magnesia. "The Hummocks" have hitherto, J 

 believe, been considered a portion of the crystalline schists which 

 are conspicuously developed farther north, and also to the north- 

 west. Occurring as they do at no great distance from the lavas of 

 the Chetwynd area, in which olivine is the chief ingredient, I 

 think it not improbable that they are also of volcanic origin, and 

 that their present structure is due to the complete serpentisation of 

 the abundant olivine they once contained. In reality, these two 



