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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 5, 



the Stinchar from the Silurian rocks of the Girvan district. One of 

 the most striking of these eruptive hills, and in form not unlike 

 Arthur's Seat near Edinburgh, is Knockdolian, on the right bank of 

 the Stinchar, which throws off one shoulder to Colmonel and another 

 to Ballantrae, whose old castle stands upon the rock. The lower and 

 seaward slopes of this trappean mountain are covered with much drift, 

 which there occupies terraces*. Geologists may, indeed, be surprised, 

 when they throw their eye over MacCulloch's Geological Map of Scot- 

 land, and observe that whilst all the tract around Girvan, which has 

 just been cited as so eminently Silurian by its fossils, is coloured as Old 

 Red Sandstone ; so in the district now under notice, not a vestige of 

 igneous rock or limestone is indicated, the whole being laid down as 

 greywacke or clay-slate ! And yet the lofty, lichen-covered vertical 

 cliffs of serpentine and greenstone, as exposed in the seaward faces of 

 Bennan Head, form as pictorial a scene of igneous rocks as any in 

 Scotland. It is in the eruptive rocks (chiefly serpentinous and dial- 

 lagic), which throw off the conglomerate, that most of the caverns 

 and chasms prevail ; and, even as an admirer of fine scenery, I must 

 regret that this grand coast section has not been sketched by a good 

 artist and made known to the public. 



Proceeding inland from the rugged headland of Bennan to its 

 equally igneous neighbour Knockdolian, a limestone, first visited I 

 believe by Mr. J. Carrick Moore, is seen to be worked at the farm 

 of Bogang, not far distant from the north slopes of the latter. Al- 

 though close to an eruptive mass, the strike of this limestone and 

 shale is nearly that of the Silurian strata of the region, and the dip 

 is to the south or towards the igneous rock. The chief mass of this 

 limestone is of very dark colour with white veins, and soapy, ser- 

 pentinous sahlbandes. The fossils chiefly occur in the alternating 

 and underlying shale-courses, and the collection we made consisted of 

 Orthis virgata, Sow., O. confinis, Salter, Maclurea magna, Hall ?, 

 Murchisonia, and a fragment of a large Isotelusf. As the Orthis 

 virgata occurs in the limestone of Peebleshire, and is there also asso- 

 ciated with a species of Isotelus, it is fair to infer that this rock of Bo- 

 gang, as well as that of Craig Head north of Girvan, is of the same 

 age as the stratum described by Professor Nicol, which he has, I 

 think, very properly referred to the age of the Llandeilo flags. 



On the left hand of the Stinchar and opposite to the village of 

 Colmonel, limestone has also been long quarried from under the old 

 castle of Craig Neil, inhabited formerly by Nigel, the brother of King 

 Robert Bruce. The rock, in which some fossils are visible, has there 

 been thrown up into a conical hummock, and, from its altered, frac- 



* The flat shore at Ballantrae also exposes nearly horizontal ledges of a very soft 

 thick-bedded, dark red sandstone (see Map), which is manifestly younger than the 

 inclined red sandstone of this coast. Although I do not pretend to define its age 

 with accuracy, I presume it must be classed with the newer Red Sandstone — a 

 very loose term — of Dumfriesshire and Cumberland. 



f Most of these fossils were first obtained by Mr. J. Carrick Moore. The col- 

 lection made by Professor Sedgwick contains one or two other fossils. The 

 Maclurea found here is a different species to that occurring at Aldeans, which we 

 have figured in PI. VIII. fig. 7. 



