Carboniferous Period in East Scotland. 249 
of this Society, made collections from it, and Heterangiwm grievi, a fern then 
new to science, commemorates his work there. The late C. W. Peach also 
worked in this bed, and obtained from it a lycopodiaceous cone, bearing both 
macrospores and microspores, which was described by the late Wm. Carruthers. 
In our own time the study of the contents of this bed has been taken up with 
great success by Dr Gordon, who has been enabled to throw much light upon 
the methods that many of the early plants adopted in building up trunks and 
branches, which enabled otherwise lowly and creeping plants to assume tree- 
like habits, and thus to outstrip their neighbours in the struggle for ight and 
for air. Dr Gordon was fortunate enough to be able to trace this rock to its 
source among the volcanic pile in Alexander’s Crag. He considers that the 
limestone, although now broken up and included in a volcanic breccia, must 
have been formed in a freshwater pool in the volcanic plateau, which must 
at that time have become subaerial. Into this pool the Upland vegetation 
growing upon the rich volcanic soil afforded by the very basic rocks of the 
plateau must have fallen, and the spring water supplied by these rocks was 
so full of mineralising matter as to replace the finest structures, molecule by 
molecule, as they decayed. The remains of such a pool are well shown in 
section on the seashore close by; for, overlying the slaggy top of a very basic 
lava and filling up all the cracks and inequalities of the floors, a few feet of 
dark almost black shale and limestone with plant remains are seen to be over- 
laid by a second lava stream, the base of which is perforated vertically upwards 
for a foot or more by a succession of cylindrical vesicles where the steam 
from the wet sediments must have risen through the still liquid lava. 
Farther to the east of Pettycur harbour, and north of the street, black shales 
occur between the flows in which Dr Gordon obtained some well-preserved 
stems, and a little farther still, above another flow, two coal seams are seen to 
crop out among fine tuffs. ) 
That an upland flora existed is shown by the well-known example of the 
tree trunk Pitys (Araucarioxylon) withami, found in the Craigleith Quarry, 
which passed up obliquely through many feet of sandstone and which must 
have been a veritable “Sawyer,” pictures of which are familiar to us. 
Each volcanic cone that rose above water seems to have harboured a small 
colony of stem-forming plants. This is indicated by the common occurrence 
of charred and mineralised fragments of wood to be met with among the 
agglomerates and other debris which fill in the underground vents or 
“necks ” now exposed by denudation, often where the whole of the ejectementa 
cast out upon the original surface has been swept away. Professor Judd, 
Mr A. Macconochie, and more recently Dr Campbell obtained such woody 
fragments in the Lion’s Head vent of Arthur’s Seat. 
