568 Notices of Memoirs — Diatomaceous Earth. 



trunks on the coast below high-water level. These are usually 

 spoken of as ' submerged forests,' and their occurrence in the places 

 mentioned may indicate a lowering of the surface of the land since 

 the trees grew. 



The present mouths of the Mersey, Alt, Douglas, and Eibble have 

 all been cut through ancient meres, and as there is evidence that 

 these formerly drained to the east it is probable that the breaching 

 of the meres has resulted in a reversal of flow since Glacial times, 

 and the present mouths are of comparatively recent date. 



The sandhills on the coast only occur in districts adjacent to 

 rivers. It is probable that they owe their origin to the material 

 brought down by the rivers, forming a bank of sand in the slack 

 water at each side of their channels. These banks drying at low 

 water, the sand has then been blown inland by the prevailing south- 

 west winds. No dunes existed in this district 400 years ago, and 

 they are probably subsequent to and result from the reversal of the 

 drainage of the Mersey and Eibble. 



V. — Diatomaceous Earth at Lake Gnangara, Western 



Australia. 



rpHE Government Geologist of Western Australia reports the 

 X discovery of an extensive deposit of Diatomaceous earth at Lake 

 Gnangara, in the Wanneroo district. It is composed almost entirely 

 of the skeletons of Diatoms, and of the spicules of fresh-water 

 sponges (Spongilla). The main deposit forms a quaking bog, with 

 a smooth surface, starting immediately at the foot of the sandy banks 

 on the northern shore of the lake at a height of a few inches above 

 ■water-level, and sloping gradually towards the lake, beneath the 

 surface of which it passes. The whole deposit is covered with 

 a scanty growth of reeds, and, from all appearances, is still in 

 process of formation. The deposit occupies the northern and 

 western edges of Lake Gnangara, a permanent fresh-water lake 

 eleven miles due north from Perth, and about four miles north-east of 

 Wanneroo. Under the microscope, the earth is seen to be composed 

 of a felted mass of siliceous spicules, in which are embedded 

 numerous diatom frustules, of perfect form. They belong mainly to 

 the groups of NavicuJece and Mmotiece, a very large species of 

 Finnularia being especially noticeable. The genus Bacillaria, which 

 is said to yield the best dynamite, is apparently entirely absent. 

 The Wanneroo earth would not appear to be well suited for the 

 manufacture of d3mamite, owing to the high percentage of alumina 

 in it, and also owing to the forms of the diatoms present in it. It is, 

 however, eminentlj^ suited for the manufacture of disinfectants 

 by the absorption of phenol, etc., as well as for lining cold- 

 storage rooms, and railway wagons, and as an ingredient for 

 refrigerating paint. Owing to the extremely small percentage 

 of iron and other mineral impurity present, it would be an 

 excellent source of silica for the manufacture of soluble and 

 other glass. It could also be used as an ingredient of metal- 



