1884-85.] Edinburgh Naturalists' Field Club. 235 



beds of feletone and felstone-porpbyiy in long bands, running north- 

 east and south-west, and apparently overlapiiing each other from 

 north-west to south-east in an ascending order. These beds or 

 bands of volcanic rock extend south-west to Habbie's Howe and the 

 west Kipp Hill, and one narrow band runs as far south as Carlops. 

 The middle portion of the Pentland Hills is mostly made up of 

 sedimentary rocks, belonging to three different formations — viz., 

 Silurian, Old Eed Sandstone, and Carboniferous. The oldest of 

 these — the Silurian — occurs as a number of x^atches cropping up 

 through the newer rocks. The first of these patches we meet with, 

 going south from Edinburgh, occurs at Craigentarrie, on the north- 

 west side of the hills, a little to the east of Threipmuir Pond ; the 

 next lies to the south of Bavelaw Castle ; another patch occurs at 

 Habbie's Howe ; but the largest and most important exposure of 

 Silurian rocks in the Pentland Hills occurs at the head of the 

 North Esk and Lyne Water. These patches of Silurian rocks are 

 separated from one another by overlying beds of conglomerate, 

 sandstone, and igneous rocks. The conglomerates and sandstones 

 lie unconformable on the Sihirian, and the unconformability between 

 these rocks is extreme, for the Silurian beds, where they are exposed 

 in the Pentland Hills, stand nearly vertical, while the conglomerates 

 and sandstones lie in a nearly horizontal position upon their up- 

 turned ends. The conglomerates that lie upon the Silurian are 

 mostly made up of rounded pieces of these Silurian rocks. These 

 pieces have evidently been broken off the upturned edges of the 

 beds, and rolled about in water and rounded in a most complete 

 manner, as can be seen in the gorge which the Logan Burn has cut 

 at Habbie's Howe, where the rounded pebbles of all sizes up to a 

 foot in diameter are exposed in cliffs from fifty to sixty feet high. 

 The beds gradually get finer as they rise in the series, till they end 

 in the sandstones of the Hare Hill and Cairn Hill. The rest of 

 the Pentland Hills to the south-west are mostly made up of con- 

 glomerates, grits, and sandstones, and the hills in that portion of 

 the range are carved out of the nearly horizontal beds. With 

 regard to the age of these conglomerates and sandstones which lie 

 in the middle and south-western portion of the Pentlands, we have 

 little data to go upon to show what system they really belong to. 

 In all likelihood the conglomerates and sandstones that lie im- 

 mediately above the Silurian, and unconformable to these rocks, 

 belong to the upper portion of the Old Eed Sandstone system ; 

 while the sandstones that flank the hills on their north-west side, 

 and the sandstones that form the hills at the south-west end of the 

 range, may be considered as Carboniferous. 



Now it is part of the geologist's work to endeavour, from the 

 facts he has gathered, to look back into the world's history, and 

 depict the changes which have taken place over the district he 



