88 Armitage, Country about West Essendon. [^^"sept!^*' 



locality on eroded stratified marine deposits of Kalimnan 

 age. 



The Sand Pits of the Horseshoe Bend. 



Resting unconformably on the considerably eroded surface 

 of the Older Basalt occur the grits, sands, and clay beds which 

 are portion of the vast deposits of Tertiary strata of Southern 

 Victoria. An open cut into this material has been made on the 

 eastern outer side of the Bend, and is known locally as the 

 *' Sand Pits." These Pits (a picture of portion of which appeared 

 in the Naturalist of last July) reveal some interesting features 

 worthy of notice. 



Near the lowest parts are beds, a few feet thick, of a coarse, 

 brown, ferruginous grit, bedded very irregularly. This is suc- 

 ceeded by a bed of fine white clay a couple of feet thick, evidently 

 a deep water deposit. Above this is a series of current-bedded 

 sands and grits, consisting mainly of angular particles of quartz. 

 These beds are about 60 or 70 feet thick, are of shallow-water 

 origin, and were probably laid down close to a shore-line where 

 currents were strong. Overlying these is a thickness of from 

 15 to 20 feet of very fine sand, which is evenly and horizontally 

 bedded, thus showing by these characters a change to quiet 

 water deposition, caused probably by a deepening of the sea 

 on the floor of which the deposits were laid down. 



Intercalated amongst the beds of coarser material are thin 

 bands of a black titaniferous iron sand, which Mr. Drew, of the 

 Chemistry School, has determined to be the variety ilmenite. 

 Other black lines occur in the beds. These, on examination, 

 prove to be thin bands of quartz grains coated with a glaze of 

 black lustrous limonite. In still other cases the black colour 

 bands show a highly splendent iridescence, and this was found 

 to be due to a combination of iron and manganese oxides, pro- 

 bably hematite and pyrolusite. 



Variations in the amount and character of the iron and other 

 salts present account for the fact that some of the beds are 

 rather firmly cemented, while others cruml)le away at the 

 slightest touch. On the whole, the beds in the Sand Pits are 

 very loosely consolidated. Along the bedding and incipient 

 joint planes, especially in the evenly-bedded fine sands near the 

 top of the series, thin red and yellow colour bands are arranged 

 fairly regularly, giving a very pleasing optical effect to the beds 

 in which they occur. These colouring materials seem to have 

 been derived from the decomposition of the Older Basalt which 

 occurred both before and after the deposition of the beds. In 

 the grit beds, for many feet over the clay stratum above- 

 mentioned, are cla}^ pebbles scattered in some profusion. 

 Sections of these pebbles, cut and examined microscojMcally. 

 show no igneous structure, while in one or two cases small quartz 



