952 DR ROBERT CAMPBELL ON 
of the Crawton group. A very poor exposure of a dolerite accompanied by similar 
types of metamorphosed tufts is seen at Mudlin’s Den, near Hallgreen, at approximately 
the same stratigraphical horizon. Numerous thin sills and narrow dykes intruded into 
the same volcanic conglomerate and tuff zone between Bervie and Todhead are 
lamprophyric in character. Their occurrence is restricted to this horizon. They are 
all much decomposed, and resemble the lamprophyre dykes belonging to the volcanic 
series of the Pentland Hills. 
The above minor intrusions belong to a comparatively late phase in the volcanic 
history of the area. Most of them are intruded into, and are therefore younger than, 
the lower portion of the Crawton group; others cut the older part of the Arbuthnott 
group. ‘There is no evidence to show that any are younger than the hypersthene 
andesite and basalt series. 
Comparing the Kincardineshire Old Red Sandstone with a typical Scottish Carbon- 
iferous succession, one is struck at once with the almost entire absence of intrusive sills. 
A few thin sills occur, but none at all comparable with the massive intrusions of 
Carboniferous age. In marked contrast again with the volcanic members of the Lower 
Old Red Sandstone of other areas,—such as the Cheviot group, or the Lorne plateau— 
is the relatively poor development of the dyke phase. The paucity of sills and dykes 
may reasonably be correlated with the absence of vents. It is worthy of note, too, 
that dykes of presumably Old Red Sandstone age show a marked increase in number 
in the belt of schists which intervenes between the Highland fault and the newer 
granites; and further, that the development of minor intrusions in the Old Red 
Sandstone area reaches a maximum at the coast line between Johnshaven and Braidon 
Bay. Such a distribution of the hypabyssal intrusions strengthens the suggestion that 
the volcanic centres were situated along two lines—one in the area now occupied by 
the Dalradian schists, the other to the east of the present coast line. 
XII. Paystcat CoNDITIONS DURING THE LOWER OLD Rep SAaNnpsToNE PERIOD. 
The Lower Old Red Sandstone of the Midland Valley of Scotland is characterised 
everywhere by the development of coarse conglomerates. A study of the succession 
in south-eastern Kincardineshire brings out very clearly two points: (L) the total thick- 
ness of coarse conglomerates is far greater than that of the finer sediments; (2) the 
coarseness of the average conglomerate is remarkable even for a Scottish Old Red Sand- 
stone district. At many horizons the boulders average about two feet; and frequently 
the magnificently rounded boulders of quartzites, granites, schistose grits, and other 
“Highland” rocks measure from three to seven feet along their longest diameter. It 
is difficult, indeed, to realise that the rounding and transportation of these boulders 
has been accomplished by the agency of moving water, either by waves or by mountain 
torrents. Not only are the blocks well rounded, but the hard, fine-grained, homogeneous 
types show remarkable curved fractures, “chatter markings,” which indicate in no 
