CHAP. XLVIII 
THE ACID DYKES AND VEINS 
441 
Within a horizontal distance of less than 100 yards three well-marked 
dykes issue from the spherulitic edge of the Meall Dearg granophyre, and 
run in a south-easterly direction in the handed gabbros (Fig. 376). The 
most northerly of these is traceable in a nearly straight line for 800 feet. 
The central dyke, which can be followed for 200 feet or more, rises as a 
band six to ten feet broad between the dark walls of gahbro as represented in 
Fig. 379. 
These dykes are marked by the most perfectly developed spherulitic and 
flow-structures (Figs. 375, 377). Numerous detached portions of other 
dykes and also irregular veins are to be observed cutting the banded 
gabbros all over the ridge of Druim an Eidhne for a distance of a mile 
or more. Many of these exhibit the same exquisitely beautiful spherulitic 
and flow-structure displayed by the dykes which can actually be traced into 
the main body of granophyre. The lines of flow conform to eveiy sinuosity 
in the boundary-walls of gabbro, and sometimes sweep round and enclose 
blocks of that rock. The example of this structure, given in Fig. 378, 
Fig. 378. — Plan of pale granophyric dyke, with spherulitic and flow-structure, cutting and enclosing 
dark gabbro, Druim an Eidhne. 
shows how these lines, curving round projections and bending into eddy- like 
swirls, exhibit the motion of a viscous lava flowing in a cleft between two 
walls of solid rock. Sometimes the laminae of flow have been disrupted, 
and broken portions of them have been carried onward and enveloped in the 
yet unconsolidated material. Certain portions of this dyke are richly 
spherulitic, the spherulites varying from the size of small peas up to that ot 
tennis-balls. Occasionally two large spherulites have coalesced into an 
8 -shaped concretion, and it may be observed in some cases that the 
spherulites are hollow shells. 
A remarkable feature has been recently observed by Mr. Harker among 
the abundant granophyre dykes and veins which intersect the gabbros and 
older rocks, along the eastern flanks of the Eed Hills of Skye between 
his contention that the acid eruptions of the Western Isles are older than the basic. Their true 
character was shown by me in a paper published in the Quart. Journ. Gcol. Soc. vol. 1. (1894), 
p. 212. 
