﻿86 



MR. G. W. TYRRELL ON THE 



[vol. lxxii, 



sandstone belonging to the 'Millstone Grit.' When the area is 

 re-mapped it is probable that these strata will be incorporated in 

 the Coal Measures. The intrusive nature of the igneous rock is 

 proved by its increasing fineness of grain towards both upper and 

 lower contacts, and by the marginal fringes of hardened sandstone 

 above and below the sill. Definitely transgressive contacts are not 

 seen, although in one place a thin band of hardened sandstone is 

 encountered about 12 feet from the upper margin of the sill. So 

 far as can be ascertained, the intrusion keeps approximately to 

 the same horizon. The whole series dips at about 10° north-west- 

 wards, and, from the width of the outcrop, the thickness of the 



Fig. 1. — Geological map of the Lugar district, on the scale of 

 1 inch to the mile, or 1 : 63,360. 



[T.P. = Teschenite-picrite ; E.D. = Essexite-dolerite sill. 

 Broken lines represent faults.] 



igneous rock is estimated at 140 feet. Apart from small irregular- 

 ities the outcrop forms a crescent-shaped strip about 3 miles long 

 and a fifth of a mile wide at its widest part. It extends in a 

 general north-easterly direction from Lugar to a mile and a half 

 beyond the village of Cronberry. The Bellow Water with its con- 

 tinuation, the Lugar, cuts through both extremities of the crescentic 

 outcrop, and gives sections at Logan Bridge on the south, and at a 

 spot a mile north-east of Cronberry on the north. The river also 

 cuts through a slight bulge of the outcrop at its confluence with 

 the Glenmuir Water. The latter stream cuts a deep trench in 

 a somewhat different direction through the intrusion at this 

 place. The outcrop is faulted continually towards the south-east 



