T. Mellard Reade — Perched Blocks near Austtticl-. 291 

 II. — The Perched Blocks op Norber Brow and their Levels 



RELATIVE TO THEIR PlACE OF OrIGIN. 

 By T. Mellard Reade, C.E., F.G.S., F.R.I.B.A. 



IN a recent excursion the Liverpool. Geological Society visited 

 Norber Brow, near Austwick, to inspect the celebrated perched 

 blocks of Silurian rock lying upon the Carboniferous limestone 

 plateau. The visit was made in very appropriate weather during 

 a storm of hail which added a weird element to the scene and 

 heightened by contrast the blackness of the Silurian blocks. Since 

 returning home I have re-read Prof. McKenny Hughes' interesting 

 paper on the subject,^ and find that generally speaking my notes 

 and measurements are in accord with his. The angularity of the 

 perched blocks, so different to the rounded and striated erratics 

 of the Boulder Clay Plains of Lancashire and Cheshire, and the 

 absence of Boulder Clay, is very striking, and inevitably suggests 

 their transportal by glacier ice probably at the last phase of the 

 glacial period. 



It has, I believe, been generally taken for granted that these 

 blocks are higher than their origin, and have been, as stated by 

 Prof. Hughes, pushed up hill from the north." Being specially 

 interested in this question, which was raised on the spot by our 

 excellent guide Dr. Eicketts, four of our party, after descending into 

 the valley, climbed up the western side and traversed it northwards 

 towards Cruramack. The first object that attracted attention was 

 a magnificent glaciated surface or roche moutonnee of Silurian rock 

 on our left ascending the slope to the west transversely to the direc- 

 tion of the valley. On the right at about the level of the perched 

 block on Norber Brow figured in Prof. Hughes's paper (p. 530), 

 which I shall refer to as Perched Block No. 1, and which we took 

 for our datum level, was what may be fitly described as a mason's 

 yard of black angular Silurian blocks, as large or larger than those 

 on Norber Brow. The bed rock was Silurian also and further 

 northward up the valley appeared to be much glaciated. Continuing 

 our ascent we reached the junction of the Silurian with the Car- 

 boniferous Limestone, and following the contour northward came 

 upon a jutting crag of Silurian from which several huge blocks had 

 separated at the joint planes a distance of a foot or two. These 

 blocks had a slight cant down hill, and were just in a condition and 

 position for transjDortal had the valley been filled with glacier ice. 

 The upper surface of the crag appeared to be rounded. The rock 

 evidently breaks up naturally into cuboidal masses. Here then was 

 probably the origin of the blocks of Norber Brow, as according to 

 the aneroid observations made by me and checked by Mr. Ashton 

 Hill, C.E., this Crag is 265 feet above Perched Block No. 1 on 

 Norber Brow. The highest point of the Silurians we tried by 

 aneroid was 295 feet above the same datum. It is evident that the 

 movement of the blocks towards Norber Brow was in accordance 



^ On some Perched Blocks and Associated Phenomena, Q.J.G.S. vol. slii. 

 pp. 527-538 (1886). ^ Q.j.G.S. vol. xlii. pp. 531 and 538. 



