THE VICTORIAN NATUKALIST, 



Description. — Mount Shadwell is a crater of uneven height, 

 broken down on the north-west and west sides. Its form 

 suggests a breached crater, considerably modified by denudation. 

 Its height is recorded as 962 feet above sea-level, and it rises 

 about 500 feet above the surrounding plains. 



The sections to which the observations in this paper refer 

 occur in two quarries on the flanks of the Mount. One is of 

 greater size than the other, so for convenience I shall refer to 

 them as the larger and smaller quarries respectively. 



Taking the larger quarry first, it is situated on the north-east 

 flank of the Mount, and abuts the western side of the road 

 running north from Mortlake to Lake Bolac. The quarry opens 

 from the north, and deepens as it extends to the south, until 

 a depth of 30 feet or 40 feet is reached. The interesting sections 

 are on its east and west faces. 



The eastern section displays a series of rocks of different 

 thicknesses. Beginning at the southern end (where the rocks are 

 the oldest) there is the following succession (see diagrammatic 

 section attached) : — 



(a.) * A considerable thickness of incoherent basaltic scoria f 

 and lapilli, mixed with blocks of basalt up to about 2 feet 

 in diameter. The scoria and lapilli are of a dull reddish 

 colour, fairly vesicular, and much decomposed. The in- 

 cluded blocks are also vesicular, and vary in colour from 

 a light dull red to an ashy white. This deposit possesses 

 no distinctly observable lines of inclination. 

 (b.) A fairly thick bed, consisting almost entirely of blocks of 

 basalt similar to those in (a), with the interspaces filled 

 with decomposing volcanic material. The dip is in a 

 northerly direction, at an angle of about 40°. This bed is 

 apparently an agglomerate, 

 (c.) An agglomerate of basalt of similar character to that in (a) 

 and (6), made up wholly of pieces of uniform size (about 

 4 inches in diameter), with no interstitial matter. It rests 

 on and possesses the same angle of inclination as (b). 



These three sets of beds belong apparently to one period of 

 time. For convenience they are hereafter collectively referred to 

 as the " red beds." In these beds Olivine, associated with its 

 ferriferous variety, Fayalite, occurs, the latter predominating. 

 (See Appendix, specimen 2.) The Fayalite has become con- 

 siderably decomposed. Pieces of Oliagoclase Andesine (specimen 

 4), often an inch in length, are also found. 



* The letters refer to the beds marked by the same letters on the diagram- 

 matic section. 



t The terms used in this paper for the fragmentary volcanic material are 

 those adopted by Prof. Gregory in his " Geography of Victoria "), pp. 183 

 et seq. 



