On Enhydros found at Beechivorth. 75 



tuents, and whether the deviations are not attended with 

 alterations of external clmracters ; the amorphous character 

 being most strongly asserted in those examples in which the 

 crystalloid is at a minimum, symptoms of the crystalline 

 character budding out whenever the crystalloid prepon- 

 derates. We may ask (experimentally, I mean) whether 

 chalcedony, which is stalactitic and dendritic, does not owe 

 this form to a proportion of crystalloidal silica larger than 

 that of agate, which deposits layer on layer on the wall of 

 the geode without any tendency to arboresce above it ; 

 whether, in other words, the agate is not deposited after the 

 manner of a varnish, while there is something approaching 

 crystallization in the form of the chalcedony. 



If this variation of habit can , be asserted for different 

 proportions of the two forms of soluble silica, it would 

 thence almost certainly follow, that with the crystalloidal 

 silica at a maximum, or rather sufficiently preponderating, 

 the deposit would assume something very nearly approach- 

 ing the crystalline form, instead of stalactitic and dendritic 

 form; it would interlace the cavity with thin planes in which 

 the crystalline character would be discernible on close 

 inspection, and the space thus being divided into regular 

 chambers, all the consequences of an inner deposit of 

 quartz crystals and other results as we find them would 

 naturally follow. The thin lamination of the chalcedony 

 exterior to the proper walls of the enhydros, the foliation 

 of the material, so to speak, appears to favour the view that 

 the property of forming plane plates resides in the material 

 itself, and is not due to moulding. 



There is, in the Melbourne Public Library Museum 

 collection of rocks, a specimen in which a chalcedonic 

 deposit has taken place, forming septa, which while 

 they are compai-able to those of the water stones, show 

 a remarkable difference, apparently very much to the 

 point in reference to what is now . suggested. In these 

 septa there is an approach to the formation of plane sur- 

 faces, but yet the deviation is so considerable as to suggest 

 an intermediate character, possibly due to an intermediate 

 proportion between the crystalloidal and colloidal silica of 

 which they are composed. 



I put forward these suggestions merely foi- what they may 

 prove worth, and as suggestive of direct experimental 

 inquiry ; and, in conclusion, I will mention a fact showing 

 that the juxtaposition of crystalloidal and colloidal quartz has 



