Extract

During field investigations carried out in the summer vacation of 1923 two relatively large unrecorded intrusions were observed in the western area of the Pentland Hills. One of these occurs as a sill in the Lower Old Red Sandstone conglomerate about one-third of a mile east-north-east of Hareshaw. The rock is exposed on both sides of a small gully, cut by one of the smaller (nameless) tributaries of the Lyne Water. The outcrop, which has a maximum vertical exposure of about 23 feet, has been traced through the conglomerate, with minor breaks, for about a quarter of a mile. Over most of the area the main sill is accompanied by a smaller overlying sill. The strike is roughly east and west, and the intruded sandstones and conglomerates are seen dipping southwards at a low angle. The sill is traversed by at least three faults of small downthrow to the west. On the upper reaches of the stream the gully narrows considerably and exposures are fewer. Some tongues or apophyses passing up into the conglomerate probably indicate the upper limits of the sill. All the exposures are very highly decomposed, and at many points the rock has weathered in situ to a fine mealy earth sometimes to a depth of two feet. Several splendid examples of spheroidal weathering indicate stages in this process of decomposition. No evidence of contact metamorphism has been observed in the intruded conglomerates, which also are in every case extremely decomposed. From the cores of some of