UNUSUAL TYPES OF PETRIFACTION. 
33 
Unusual Types of Petrifaction from Dandarragan. 
By Edward S. Simpson, B.E., F.C.S. (Read Novem- 
ber 14th, 1911.) 
Plates XII and XIII. 
Recently the present writer has studied the micro- 
scopically perfect conversion of fragments of coniferous wood 
of Mesozoic age into fluor-apatite (fluophosphate of lime) 
and dufrenite (hydrous phosphate of iron) at Dandarragan. 
The latter, so far as can be ascertained, has never been 
recorded as the petrifying agent of plant tissue, whilst the 
former is apparently of somewhat rare occurrence. These 
unusual types of petrifaction seemed, therefore, to be 
worthy of detailed description. 
In modern works on Palaeontology but little space is 
devoted to agents of petrifaction, and none whatever to 
the chemical processes involved in the molecular replace- 
ment of the various organic constituents of plant tissues by 
mineral substances of more durable nature. Even in 
F. W. Clarke’s “ Data of Geochemistry,” a work otherwise 
so complete in its review of this branch of science, this 
interesting and important geochemical subject is entirely 
ignored, except for a slight passing reference in connection 
with the discussion of an entirely different question. 
In this paper we are concerned simply with that limited 
section of the study of petrifaction which deals with the 
mineralisation in microscopically perfect detail, of the 
trunks and limbs of plants. Of the many minerals which, 
by molecular replacement of the tissue of wood, have pre 
served for us, more or less perfectly, through many geo- 
logical ages, the original structure of the timber, the most 
common in Australia are the various varieties of quartz, 
coal and calcite. 
Of plant petrifying agents in the Northern Hemisphere 
the most complete account available is contained in Solms- 
Laubach’s “ Fossil Botany.” From this work the following 
extracts are taken* — 
" Very various bodies occur in nature as agents of petrification. 
Among these silicic acid (in the form both of opal and of chalcedony) 
has the first claim to mention here. . . Silicified woods arc found in 
extraordinary quantities in all formations. . . The next in order of 
importance are the isomorphous carbonates of calcium, magnesium 
and iron, CaCOii, CaCOg + MgCOs, FeCOs. Goeppert is of 
opinion that calcium carbonate is present in some petrifictions in the 
form of aragonite, it occurs in most cases as calcite. . . Petrifactions 
in carbonate of iron very commonly form the nucleus of clay ironstone 
nodules. Wood petrified in fluorspar is very rarely found. . . Petri- 
faction in gypsum is still more rare. , . Calcium triphosphate is also 
* Solms-Laubach, H. Graf zu : Einleitung in die Palaeophytologie, 
Leipzig, 1S87. 
