GET^^DLET — 



GEOLOGY OF THE TSLE OF MA^T. 



175 



by practical men would be rewarded by the discovery of gold in re- 

 munerative quantities. Garnets, of a small size, are found at Greeba. 



Eesting upon the upturned edges of the older schists are found, on 

 both sides of the island, some very interesting deposits of the Devo- 

 nian period. Of the intervening Silurian beds but few traces now 

 remain 'among the Manx rocks. Of their former existence, however, 

 we have satisfactory proof in the fact that water-worn pebbles of 

 Silurian age, containing characteristic fossils, enter largely into the 

 composition of the overlying Old Red, particularly near Peel. The 

 Devonian rocks lie unconformably upon the underlying Cambrian 

 schists. At Langness, where this unconformability of the two series 

 of rocks is beautifully exhibited, while their strike is almost identical, 

 their dip is opposed — the schists dipping S E. at a high angle, and 

 the overlying Old Eed dipping N.W. at an angle, in this place, 

 almost equally high. They attain their greatest development to the 

 north of the central ridge near Peel, being there several hundred feet 

 thick, — principally of a workable sandstone. The venerable castle 

 and a great part of the town of Peel are built of it ; but it forms a 

 very indifferent building material, being very soft, and decomposing 

 rapidly bj the action of the atmosphere. It is in the southern basin, 

 however, near the ruins of Rushen Abbey, and along the west coast 

 of Langness, that the rocks of this formation present their most in- 

 teresting features, and where their relations to the underlying schists 

 and the overlying limestone can be best observed. Proceeding along 

 the western shore of Langness, the schists, here of a deep claret 

 colour, are seen underlying the Old Eed, and dipping inland (S.E.) 

 at a high angle, much contorted; while the Old Red itself dips sea- 

 ward (■S'.W.) at an angle equally high. The junction of the Old Red 

 with the overlying limestone is not well developed in this locality, still 

 by a little careful management it may be traced in the north-eastern 

 corner of the bay, and the direction and intensity of their dip may 

 be seen to be identical. The Old Red, as developed in this locality, 

 is a coarse conglomerate of quartz and other pebbles, many of them 

 of considerable size, enclosed in a red clayey matrix. It attains a 

 considerable thickness, but, so far as my own observations extend, 

 contains no fossils. It is possibly the equivalent of the conglomerate 

 beds of the typical " Old Red" of Herefordshire, etc. 



Purther inland, near the ruins of Rushen Abbey, founded in 1134 

 by the Cistercian monks of Purness, we may trace the passage of the 

 Devonian beds into the overlying Carboniferous limestone with 

 greater accuracy. The conglomerate has here lost its characteristic 

 red colour, and appears as a thin bed of very small white quartz 

 pebbles in a limy matrix, enclosing the characteristic fossils, princi- 

 pally OrtJiis Sharpei, of the lowest Carboniferous rocks. About a 

 mile higher up the Silverburn, near Athol Bridge, the passage of this 

 grey conglomerate into the dark limestones and shales of the lower 

 Carboniferous beds may be distinctly traced. The same appearances 

 are also very clearly seen in ascending the Brough, a low hill over- 

 looking the romantic valley of the Santonsburn, about two miles 



