210 Proceedings of Royal Society of Edinburgh. [sess 
tioned that, when this paper was read, Mr Cadell cited a case in his 
own collieries at Bo’ness. A bed of dolerite one foot in thickness 
had been intruded into a three-foot coal seam, and it left one 
foot of coal above and another foot below : one foot of coal had 
disappeared and one foot of dolerite had taken its place ; the 
upper surface of the seam remaining three feet above the lower, 
just as if no dolerite were present. Mr John Smith of Kilwin- 
ning, amongst other practical men, has furnished me with a 
similar instance which occurs in a quarry 350 yards N.E. of 
Dykeneuk farmhouse. Fig. 13 is an outline taken from Mr Smith’s 
sketch sent to me. It may be added that my colleagues Mr Grant 
Wilson, Dr Peach, and others have assured me that these are 
typical cases. Mr Dron, the author of an important work on the 
Scottish Coal-fields, has mentioned other cases. I would specially 
mention the cases illustrated by figs. 24 and 25 in the Survey 
Memoir on the Geology of Central and Western Fife. 
Lastly, a reference may be made to two of many cases that might 
be cited in which a dolerite sill invades schistose rocks. Fig. 14 
is traced from a photograph by Dr Bernard Stracey, F.G.S., and 
is from near Beinn Iadain, Morven. It shows well the abrupt 
termination of the sill against quite unbroken schist. The other, 
fig. 15, is from Torr na Sealga, Ross of Mull, from a photograph 
by Mr David Russell of Markinch, and a drawing made on the 
spot by myself. 
We may now consider a few cases in which the relationship 
of dykes to the country rock can be made out. The current 
belief in regard to these certainly is clearly enough expressed in 
nearly all treatises on the subject. The relationship implied in 
these statements may be well illustrated by taking a row of books, 
placed on edge and side by side, to represent the country rock, 
and then by intercalating other books here and there between 
them. This illustration makes it clear that there must be a 
lateral shift corresponding in amount to the aggregate width of 
the volumes intercalated. If a small book happens to be thrust 
between the leaves of a large one in the row the pages are sepa- 
rated from each other to an extent determined by the size of the 
smaller book in question, just as was illustrated by the “ intrusion ” 
