CHAP. XX 
AYRSHIRE ERUPTIONS 
335 
the structure of the terminal portion of a highly viscous lava which was 
shattered into fragments as it moved along under water. 
No clear evidence of the sites of any of the volcanic vents has yet been 
detected iu the Old Red Sandstone of Ayrshii’e. Possibly some of the 
numerous felsitic bosses to the south-west of Dalmellington may partly mark 
their positions. But the sills connected with the volcanic series are well 
exposed in the 12 miles of hilly ground between Dalmellington and Barr. 
Two groups of intrusive sheets may there be seen. The most numerous 
consist of pale or dark-pink felsite, often fidl of crystals of mica. They 
form prominent hills, such as Turgeny, Knockskae and Garleffin Fell. The 
second group comprises various diabase-sheets which have been intruded 
near the base of the red sandstones and conglomerates, over a distance of seven 
miles on the north side of the Stinchar Valley above Barr. They attain 
their greatest development on Jedburgh Hill, where they form a series of 
successive sills, the largest of which unite northwards into one thick mass 
and die out southward among the sandstones and conglomerates. 
