1903 - 4 .] Mr J. G. Goodchild on Intrusive Bocks. 
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most extremity, and which has so often been likened to the stem 
of the mushroom of which the Crag forms the cap. In this 
sandstone there are several examples of the same nature. In 
connection with the dolerite sills which give rise to the beautiful 
scenery around Hawk Crag, Aberdour, there are many remarkable 
and most instructive examples of the same kind. Some are to be 
seen at the foot of the crag N.N.E. of the outer end of the stone 
pier; but the best occur just above high-water mark on either 
side of the base of the pier. The sedimentary rocks consist of 
carbonaceous shales and sandstones belonging to some part 
of the Oil Shale subdivision of the Lower Carboniferous Rocks. 
The rocks on the north side of the pier base are chiefly sandstones. 
The dolerite has tunnelled its way into these rocks in several 
places, so that it now occurs in apparently isolated masses entirely 
enclosed within sandstone. These are shown in fig. 5, which 
is from a photograph taken by Mr Stenhouse. One of these was 
got out, and is now exhibited in the Collection above referred to. 
At the roadside facing the south edge of the pier occurs a bank 
of shale which is traversed by at least nine small sheets and 
wedges of dolerite. In a generalised way this also was figured by 
Hay Cunningham (op. cit ., PL XIY., and here, drawn from a 
photograph, in fig. 7). It is an excellent example of the manner 
in which bands of dolerite interdigitate amongst the strata near 
where rapid variations in the thickness of the intruder are taking 
place, or near where it is dying out. Amongst these tongues or fingers 
are several which end off abruptly against unbroken shale. One 
of these, which is in the Edinburgh Museum, is shown in fig. 6 ; 
while the irregular junction of the larger mass in the east side of 
the harbour with the sandstone beneath, taken from one of Mr 
Stenhouse’s photographs, is shown in fig. 8. Fine examples of 
this lateral passage by interdigitation of an intrusive mass into 
the country rock may be observed also at the west face of The 
Dasses, in the Queen’s Park, about midway between The Washing 
Green and The Piper’s Road. It is quite a common occurrence 
for sheets of dolerite (and also sills of other kinds) to end off by 
interdigitation in this way. A good example is that presented by 
the dolerite sill which forms Fair Head, on the coast of Antrim. 
In Geikie’s Ancient Volcanoes , vol. ii., p. 304, fig. 317, is given a 
