212 Proceedings of Royal Society of Edinburgh. [sess. 
Fig. 21 is traced from a photograph by Miss M. K. Andrews of 
Belfast at a quarry in the Upper New Bed Sandstone of ScrabO' 
Hill, County Down, in which some dolerite sills of Tertiary ago 
traverse the sandstone without the intrusion being accompanied 
by the slightest evidence of any mechanical disturbance, or of any 
“ laccolitisation ” of the overlying strata. The sills are traversed 
by a later dyke, as shown. 
Basic dykes and sills have been considered first in relation 
to the country rock because they are of more common occurrence. 
But it can easily be shown that precisely the same inter-relation 
exists also in the cases in which rocks of a more acid type are 
concerned. There is only one acid intrusion of any size near 
Edinburgh, which is that of the microgranite of Black Hill in 
the Pentland area. This, geologically, is an intrusive mass of 
Devonian age, which appears to represent a subterranean mass of 
the more acid type of rock whose lavas form the trachytes of the 
Caledonian Old Bed Volcanic Series of the Pentlands. It has 
evidently been formed at a late period in the history of tho 
Pentland volcanoes, and has been intruded into, amongst other 
rocks, the conglomerate which lies at the base of the volcanic 
series. Close to Logan Lee Waterfall its relation to the con- 
glomerate can be easily examined. At several places its upper 
surface has welded itself to the old gravel which forms the con- 
glomerate referred to, and the union has been so firm that many 
patches of the conglomerate may be observed still adhering to the 
face of the granitic rock. At the foot of Logan Lee Waterfall 
the conglomerate is much hardened, and veins and protrusions of 
the microgranite traverse it in exactly the same manner as in the 
cases of the basic intrusions already described. The veins are 
not easily photographed, though they are readily seen on the 
ground. But the relationship between the one rock and the 
other may be seen to- be of exactly the same kind as that so- 
wed illustrated by Mr Griffith Williams’ beautiful photograph in 
the Brit. Assoc. Series (G. J. W. 603), of the case which occurs, 
at Tan y Grisiau, in North Wales. Mr Williams kindly 
outlined the granite protrusions upon a print of the photograph 
and sent it to me, and a tracing made over these lines is given 
here on fig. 23. Field geologists must be fully aware that the 
