90 ME. GAEDINER AND i>EOF. EEYNOLDS ON THE [Feb. I912, 



A third band can be traced for some 250 yards in a north-north- 

 easterly direction along the eastern base of Knoeknamuck. All 

 these three bands are clearly -sills. A fourth, but much smaller, 

 intrusion occurs at the western end of Knoeknamuck. These sills 

 are all on the same horizon. 



{d) The Dolerites. 



Thirty-three dolerite intrusions have been mapped, aud it is 

 probable that others may not have been detected. Of these, 

 seventeen are in the Calcareous Plags (Finny School Beds), and seveji 

 in the overlying Doon Hock Grits. Five occur in the spilites, two 

 in the breccia, aud one in the Red Sandstone ; lastly, a dyke starting 

 in the breccias penetrates the basal Silurian conglomerate and one 

 of the labradorite-porphyrite sills ending in the bostonite. The 

 great majority of tliese intrusions occur in the area north and 

 west of the Doon Eock. 



The dolerites are readily divided into two groups : a larger group, 

 the strike of which ranges from west- south-west to south-south- 

 west ; and a smaller group striking south-east or south-south-cast. 

 All these rocks are dark green or grey on the freshly broken 

 surface, and weather to a rusty brown. 



Group (rt). Those Avith a vv^est-south-west to south- 

 south-west strike. — The great majority of these occur in the 

 Calcareous Flags and overlying grits, especially in the region west 

 of the Kilbride burial-ground and north of the Doon Rock ; none 

 were met with in the western part of the outcrop of these rocks 

 nearer Finny. These intrusions, which vary in length from a 

 few yards up to some 300 yards, are probably all sills. Their 

 thickness is inconsiderable, 35 feet beiug probably the maximum, 

 and they have not produced any appreciable alteration in the ad- 

 jacent strata. In rare cases doleritic intrusions belonging to gi-oup 

 \a) are met with in rocks other than the Calcareous Flags and 

 grits. Thus, one occurs in spilite a quarter of a mile south-west 

 of the top of Knock Kilbride ; a second in breccia half a mile west- 

 south-west of the same point ; and a third in red sandstone half a 

 mile north-east of Finny School. 



Group (6). Those with a south-easterly or south- 

 south-easterly trend. — These are in the main dykes, not sills, 

 and occur principally in the spilite. They are far less numerous 

 than group (a). About 300 yards south-east of Lough Mweelaun 

 a dyke 8 feet wide is seen running up the hillside, Avhich is here 

 very steep. Being covered with white lichen, it contrasts strongly 

 with the other rocks and forms a prominent feature. It is intruded 

 into spilite, and shows well-marked chilling at the edges. 



On the southern side of the ridge, almost on the line of strike of 

 the dj^ke just described, occurs another equally well-marked one, 

 which is particularly interesting on account of the variety of rocks 



