SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 889 
the chert-band in Trench No. 1 commences with the bed marked A". This bottom 
region of the chert is of special interest, since all the species of vascular plants and 
practically all the types of Thallophyta found in the deposit have been met with in 
its thickness of 1 foot 3 inches, and indeed in the lower portion Bed A"l. The basal 
region consists of a pure accumulation of Rhynia Gwynne-Vaughani, usually in a 
clear peaty matrix. Occasionally sporangia of R. major have been met with in the 
peat thus formed. Above this came a peat formed of more or less decayed Hornea 
Lignieri, rhizomes, stems, and sporangia of this plant being present. In the upper 
portion of this region Rhynia major is associated with the Hornea (Part III, fig. 2). 
Overlying this Hornea peat came a sandy bed enclosing remains of Asteroxylon 
and some Hornea. The Asteroxylon was best preserved immediately above the 
Hornea peat, and its rhizomes extended down into the latter, penetrating portions 
of the plants (Part III, fig. 2 ; Part IV, fig. 24). On passing further upwards into 
the dark sandy Bed A"2 the preservation of the stems of Asteroxylon embedded in 
the sandy matrix is less good. 
While this is the succession shown in one block at this particular spot, other blocks 
known to have come from the same level at no great distance show that it was not 
invariable. Thus in one block a clear peaty matrix with stems and sporangia of 
Hornea mixed with rhizomes, stems, and intermediate regions of Asteroxylon came 
in place of the pure Hornea peat. Another block had the typical Rhynia Gwynne- 
Vaughani peat below, and above this well-preserved Asteroxylon in a clear peaty 
matrix. A very similar block had the Rhynia Gwynne-Vaughani peat, below 
followed by a zone with Asteroxylon only, while another thin layer of Rhynia 
Gwynne-Vaughani came above this. With the exception of this last specimen, peat 
composed of R. Gwynne-Vaughani has only been seen at the extreme base of this 
bed. It was not met with above Bed AM in the section studied. 
In view of the limitation of R. Gwynne-Vaughani to the base of the section of 
the bed as exposed in situ, it is convenient to refer in this place to two loose blocks 
of particular interest. One of these is the cubical block, from the weathered face of 
which fig. 2 in Part I was taken. This block, which is now in the Natural History 
(British) Museum, proves that at some places in the bed there was an accumulation 
of pure R. Gwynne-Vaughani peat to a depth of at least 12 inches. The other is the 
block represented in Part I, fig. 5, in which the closely associated, tapering stems of 
R. Gwynne-Vaughani stood practically erect, as they had grown above a peat 
composed of the remains of the same plant. 
Returning to the description of the section from Trench I, it is to be noted that 
following on Bed A "2 came a definite band of cherty sandstone of some thickness 
(A"3, A'). This had streaks of carbonaceous matter, but, owing to the absence of 
plant-remains showing structure, it was not studied in detail. 
The thick Bed B 6 again exhibits peaty structure, being composed throughout of 
plant-remains with their form and structure fairly well preserved. These lay in a 
