182 
PROFESSOR T. J. JEHU AND DR ROBERT CAMPBELL ON 
black and greyish amorphous material, probably carbonaceous and ferruginous. 
Conspicuous also are circular and oval areas of chalcedony, representing doubtless 
casts of radiolaria. The “lattice-structure” of the radiolaria is not seen in thin 
section, but may often be detected in hand specimens (Plate I, fig. 13). Pyrites in 
nodular form may sometimes be observed, and with high powers minute flakes of 
authigenous mica and thin needles of rutile are seen to occur sporadically. Clastic 
terrigenous material is absent. The typical cherty mudstones and shales have as 
their chief constituents small, colourless, authigenous micas, and granular, finely 
crystalline or crypto-crystalline chalcedony. They are invariably crowded with tiny, 
brownish, hair-like needles of rutile. Pyrites in small cubes and nodules and 
irregular patches of carbonates also occur. Radiolaria are less conspicuous than in 
the cherts. Mudstones and shales with little or no free silica are of infrequent 
occurrence. Like the cherty mudstones, they are crowded with rutile needles. 
Their distinctive character lies in the presence of a fairly large proportion of 
recognisable clastic material in the shape of grains of quartz, muscovite, and zircon. 
The dominant sediments are the black shales and the cherty shales and mudstones. 
The cherts are characterised by their richness in radiolaria, and by the absence of 
terrigenous material ; the more muddy types by the comparative scarcity of radio- 
laria, by the abundance of rutile needles, by the occasional presence of clastic grains, 
and in the case of the black shales by the abundance of carbonaceous matter. Most 
of the mica, the rutile, and the chlorite are doubtless in every case authigenous. 
The pure cherts evidently represent radiolarian oozes which accumulated under dear- 
water conditions ; the interbedded spilites are the product of contemporaneous 
submarine volcanic eruptions, and the cherty shales and mudstones bespeak deposi- 
tion at or near the margin of an area of terrigenous sedimentation. 
Y. The Rocks of the Upper or Margie Series. 
The rocks of the Margie Series are sharply contrasted with those of the under- 
lying Black Shale and Chert Series. Grits form the dominant type of sediment, and 
the shales which, in the Aberfoyle area, are relatively unimportant, are accompanied 
by limestone, never by cherts or cherty shales and mudstones. 
The Basement Breccia . — At the base of the series occurs a remarkable breccia, 
best seen in the neighbourhood of Clashbeg Wood, but exposed also to the 
west of the Bofrishlie Burn fossil locality, again near a small stream about 300 
yards north-east of the ruins of Bofrishlie Farm, and also about one-third of 
a mile further east midway between Kirkton Hill and the Pow. In the western 
part of the area it appears along the southern margin of the first spilite outcrop to 
the west of the Kelty Water. It is found as the basement member of the series on 
both sides of the ridge formed by the underlying black shales and cherts (see 
Map, Plate VI). 
The most striking feature in the breccia at Clashbeg Wood is the presence of 
