S28 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



north-westward, and appear at low-water in the ridge upon which 

 the Derby Haven Breakwater is built. The intersection of these 

 dikes with the greenstone is also obscure, being either built over as 

 at the bridge connecting Fort Island with Langness, or covered up 

 by sea-weed and shingles. 



Before leaving Langness, we must notice the remarkable mass of 

 greenstone on the summit of the hill at its northern extremity. This 

 mass appears pushed up amongst the schists which mantle round it, 

 and into which it sends forth arms in every direction. It is most ex- 

 tensively though irregularly developed in a westerly direction along 

 the ridge. Starting again from the southern end of the Derby Haven 

 Breakwater in a north-easterly direction, we follow an anticlinal 

 upon which the breakwater is built, and which is intersected nearly 

 at right angles by the two trap-dikes which have just been men- 

 tioned. At the northern end of the breakwater the first observable 

 boss occurs, and a little further north-eastward, near the old limekiln, 

 amongst divided and broken beds, we may make out another. The 

 limestones here are sometimes greatly altered, especially along cracks, 

 and the sequence into the Old red conglomerate may be observed, 

 although it is interrupted in one place by the interesting tabular 

 mass of trap before mentioned. At that spot (see Map, PI. XVI.) 

 the trap has so mixed itself with the Old red conglomerate as to ap- 

 pear a substitute for the ordinary matrix of the quartz pebbles. The 

 strike of the beds is here S. 50° W. mag. At the southern extremity 

 of the little bay of Ronaldsway, there may be traced the effects of 

 a disturbance crossing the general strike of the beds, and forming 

 troughs on the northern and southern sides. This line of disturbance 

 runs from under the drift in a direction N. 80° E. mag. for a distance 

 of sixty yards, and then gradually disappears. Along the ridge of this 

 anticlinal the limestone is raised vertically, but the steeper beds are on 

 the northern side. Very unequivocal tokens are here given of igneous 

 action, the limestones are crystalline and corroded, and we even have 

 patches of the overlying boulder-clay formation so hardened and 

 cemented together as to have resisted the denuding action of the 

 sea. This may have been caused by heated gaseous vapours ascend- 

 ing through the cracks formed by a previous disturbance, but it 

 tends to support the opinion which I shall have occasion to put forth 

 in the second part of this communication, that the series of disturb- 

 ances thus noticed and the phEenoraena connected with them are of 

 a date posterior to the formation of the boulder-clay, vs^henever that 

 might be. It will be observed that we have several cracks and slight 

 faults running in directions parallel to this, and traceable hence 

 to Coshnahawin at the mouth of the Santon river, but I can only 

 at present direct attention to the fact, which is Avell- worthy of careful 

 consideration. This little bay of Ronaldsway will be found the most 

 fossiliferous of all the localities in which the lower dark-coloured 

 limestones are accessible. There is one bed of mudstone enor- 

 mously loaded with fucoids, another (a shaly bed) abounds with 

 encrinital stems, and in a third Orthis Sharpei is found. Two more 

 of these bosses occur in Ronaldsway Bay, and as we proceed north- 



