L. A. Necker de Saussure Voyage en Ecosse. 183 



clay, and secondary limestone; but a little further north, the 

 micaceous schists and granites commence. If a line be drawn 

 from east to west, through the castle of Brodich we shall have 

 approximatively the geographical limit of the primitive and 

 secondary rocks. A third formation very frequently appears 

 in the southern portion of the island; namely, that of trap, 

 which is found sometimes in rounded cones, standing on the 

 top of secondary hills, and sometimes under the forms of 

 large and extended veins, (whin dykes) which intersect their 

 strata. These veins stretch occasionally even into the pri- 

 mitive rocks, grunstein, basalt, clinkstone, pitchstone, and a 

 peculiar porphyry, constitute the rocks of the Arran trap- 

 formation. 



The relative position of the three rocks, sandstone, pitch- 

 stone, and clinckstone, which occur near the wood of Brodich, 

 is difficult to determine. The pitchstone seems disposed rather 

 in great detached blocks, than as forming beds or veins. It 

 appears at one time above, and another below the sandstone, 

 ■which is greatly indurated in its neighbourhood. The clink- 

 stone is also spread up and down, apparently without mutual 

 connexion. Some miles to the south of Brodich, on the way 

 to the larger village of Lamlash, we find a vein of pitchstone 

 of a bottle-green colour, which crosses the road. Its width is 

 eight feet. A rivulet which passes near the road, has laid 

 open a portion of this vein, and has shewn it to be accompanied 

 by a collateral vein of clinkstone, which here separates the 

 pitchstone from the sandstone strata, which compose this 

 platform. On travelling further to the southwards, we come to 

 the hills of Dunfeune and Dundou, the most elevated summits 

 of the promontory which separates the two bays of Lamlash 

 and Brodich. The lower part of this promontory is composed 

 of red sandstone, and of a breccia, having for its basis the 

 same sandstone, which forms the rocks and clifts on the sea- 

 shore, as well as the lofty hills on which are built the hamlet 

 of Corygills. 



On this sandstone there rests a mass of trap of a porphyry 

 with a petrosilex basis, which occupies the summits of Dun- 

 peune and Dundou, exhibiting very regular prismatic columns. 

 Veins of pitchstone and basalt, and beds of greenstone occur in 

 great abundance, in the strata of sandstone and breccia which 

 form the basis of these hills. 



Mr. Necker thinks that the trap-rock which caps the above 

 eminences, has been improperly taken by Mr. Jameson for a 

 porphyry with a basis of wacke, from which it differs essen- 

 tially, in hardness, fracture, and its habitude with the blow- 

 pipe. This beautiful rock is a porphyry formed by three very 

 distinct elements: 1st, A homogeneous paste of feldspar or pe- 

 firosilex; 2c/, Crystals of quartz; 3c/, Crystals of feldspar. The 



