894 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
position in which their remains are found ; it is possible, though not certain, that in 
other cases the remains may have accumulated in water from plants growing close 
by. The structure of the resulting mass, excluding the sandy bands, agrees with 
that of recent peats in the absence of mineral particles and the presence of a matrix 
embedding more or less well-preserved portions of plants. The matrix, though in 
great part amorphous, must have had sufficient consistency to support the fragments 
of tissues, spores, etc., evenly distributed through it. The decay of the plant- 
remains is to be associated with the presence of saprophytic fungi in them, and 
doubtless also with the action of bacteria. It seems to have taken various forms and 
to have been arrested at various stages. The arrest may have been related to 
absence of oxygen ; the more thorough decay in relation to the admixture of sand 
supports this view. Hyphse and resting-spores of fungi are chiefly found in relation 
to the plant-remains, and when they occur in the matrix were probably in great part, 
though not entirely, set free by the decay of the plants. 
All these features find close parallels in recent peats, especially when the 
structure of the latter is examined in microscopical sections. The component plants 
are, of course, quite different, and the fungi do not belong to the same types. 
Persistent dark hyphse and resting-spores and sclerotia occur abundantly in the 
plant-remains and the amorphous matrix of recent peats. Recent peats, however, 
become more amorphous on passing downwards, and the difference in this respect of 
the Rliynie deposit will require to be considered below. 
The presence of numerous layers of sand interrupting the peat in the Rhynie 
deposit is a feature in which it differs from most recent peats. We have no definite 
evidence showing that this sand was wind-borne, and therefore suggested frequent 
inundations to account for the irregular layers of sand, and more prolonged sub- 
mergence to account for the more definite sandstone beds. The possibility of some 
of the sand having been wind-borne must, however, be kept in mind. This applies 
especially to the irregular sandy layers and the scattered grains in the matrix of the 
peat. The dark colour of these regions appears to be due to the altered vegetable 
matter ; decomposition seems to have been complete and rapid in the sandy layers. 
The vegetable remains thus represented in the layers of sandy matrix must corre- 
spond to a considerable thickness of the peat, any remains of stems, etc., that persist 
being almost completely flattened. 
Since the Rhynie deposit occurred in what is known to have been an actively 
volcanic region, it is reasonable to regard the silicification of the bed as in some 
way due to water containing silica in solution, possibly derived from fumaroles. 
The separation .of silica in the colloidal form may have been determined, in part 
at least, by the decaying plant-remains. Such a deposition of silica is known to 
follow from the growth of Cyanophycese and Bacteria, and around decaying organic 
material in hot springs. The Rhynie chert may have been the result of a some- 
what similar process. 
