A Process for the Mineral Analysis of Rocks. 417 



rocks consist of sandstones, slates, calcareous flags, ashes and ashy 

 conglomerates, rhyolitic lava-flows, and various intrusive rocks. The 

 general structure is an S-shaped fold, inverted towards the north so 

 that the dip of the beds is approximately south-easterly, and the oldest 

 beds occur to the north, at Coosglass. Both anticline and syncline 

 are faulted, and a patch of Old Red Sandstone is caught in under 

 the synclinal thrust at Coosmore. Fossils, mainly corals, brachiopods, 

 lamellibranchs, and gasteropods, are fairly abundant ; but trilobites 

 are rare and graptolites absent. The whole of the fossiliferous rocks 

 are of Silurian age ; the majority of those exposed on the coast are of 

 Wenlock or Wenlock-Llandovery age, while the majority of those 

 exposed inland are of Ludlow age. The general classification is as 

 follows : — 



Lower Devonian ... Dingle Series. Feet. 



T f 5. Croaghmarhin Beds : calcareous sandstones 



^ UDL<m 1 and flags of Ludlow age ? 1000 



f 4. Drom Point Beds about 600 



i 3. Bed sandstones and ashes, with green ash 



w J at the top 350 



" ) 2. Clogher Head Series : calcareous flags and 

 slates, with abundant contemporaneous 



igneous rocks 550 



, T . T I 1. Ferriter's Cove Beds : chief! v calcareous flags, 



\\ E.NLOCK - LLAXDO- .-., u j- * j ' l j. J t 



s witb a subordinate development ot contem- 

 very. • , r oonn 



poraneous igneous rocks _'o(JU 



? Sinerwick Beds. 



Contemporaneous volcanic rocks are first met with low down in the 

 Wenlock-Llandovery Series, and reach their maximum in the Wenlock 

 Series, especially in the southern part of the area. There are ashes 

 but no lavas in the Ludlow. The volcanic rocks are all of acid 

 character, and include nodular, banded, and non-banded rhyolites, 

 with tuffs and ashes both coarse and fine. The Dingle Beds appear 

 to be conformable, but movement occurred before the Old-Red- 

 Sandstone Conglomerate was laid down, and the overfolding and 

 thrusting probably took place during the post-Carboniferous period 

 of earth-movement. Before the last movement fine-grained diabasic 

 rocks (' greenstones ') appear to have been intruded. The thickening 

 of the volcanic rocks to the southward seems to indicate that the 

 vents must have been situated in this quarter. The beds as a whole 

 were deposited in shallow water in the proximity of land, and they 

 point to the existence of rocks, such as granites, not now known at 

 the surface in the district. 



2. ' A Process for the Mineral Analysis of Rocks.' By William 

 Johnson Sollas, D.Sc, LL.D., F.R.S., F.G.S., Professor of Geology 

 in the University of Oxford. 



The method proposed is to obtain a quantitative estimation of 

 the mineral composition of a rock, and from the known composition 

 of the minerals to calculate the percentage-composition of the rock. 

 The specific gravities of the minerals are first determined by means 

 of a diffusion-column of methylene-iodide and beads of known 

 specific gravity, and the presence or absence of particular minerals 



