420 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 22, 



very few pebbles of quartz. The size of these fragments varies from 

 that of peas up to blocks of a ton or more in weight, the general size 

 being that of ordinary sea-shore shingle. These are frequently 

 cemented by carbonate of lime, and in some instances by hsematitic 

 matter. Where the blocks are largest the chffs in general readily 

 crumble down, the masses being incoherent from want of a proper 

 mixture of sand. Where the latter is in sufficient quantity, the result 

 is a very hard and tenacious rock. All the materials of which the 

 conglomerate consists appear to have been derived from the adjoining 

 greywacke and porphyritic rocks, chiefly those lying to westward. 

 The dip of the beds is almost invariably nearly E.N.E. at angles vary- 

 ing from 0° to 20° or 30°, and averaging perhaps about 10°. In one 

 or two places, however, in the immediate vicinity of dislocations, the 

 direction and amount of dip are considerably changed. 



A remarkable feature connected with this formation of conglome- 

 rate is the occurrence therein of numerous veins or dykes of a species 

 of claystone which has been pom-ed from below, in a state of fusion, 

 into fissures, which appear to have been opened during the elevatory 

 process by the subjacent fluid matter strugghng to obtain an outlet. 

 This claystone is of a brown or drab colour, hard, and frequently very 

 porous, apparently destitute of augite, but occasionally showing 

 crystals of quartz and haematite, together with a little earthy chlorite. 

 In the numerous ravines which intersect the conglomerate I have ob- 

 served twenty-six of these dykes, and this is probably but a small 

 part of the whole. (See map, in which the positions, and, as far as 

 possible, the directions of some of these claystone dykes are laid down.) 

 They strikingly resemble each other in almost every respect. The 

 great majority are about 3 feet thick, but one or two are under 1 foot ; 

 whilst one is 15, and another not less than 33 feet in thickness. 

 They are generally nearly vertical, but undulate a little both vertically 

 and horizontally. Their directions are almost in every instance 

 W.N.W. to E.S.E., or at right angles to that of the trough in which 

 the conglomerate has been deposited. The alteration produced upon 

 the conglomerate adjoining these dykes is very interesting, showing 

 in a very striking manner the intensely-heated state of the molten 

 claystone at the period of its eruption. On each side of the 33-feet 

 dyke the conglomerate has been fused to a distance of a few feet, 

 beyond which the half-melted pebbles begin to be distinguishable. 

 The smaller dykes have melted down all the projections of the walls 

 of the fissures which they occupy. The central and deeper-seated 

 portions of these dykes are more compact and crystalline, showing 

 quartz and heematitic crystals, whilst towards the surface they become 

 very porous and slaggy. 



Fissures other than those occupied by the dykes above described 

 are of frequent occurrence in the conglomerate. In Shippith Glen a 

 great number of minute fissures are seen running in a W.N.W. or 

 N.W. by W. direction. The *glen' itself is merely a deep ravine 

 with very precipitous sides, and so narrow at bottom that in many 

 places a person cannot force a passage. It is about 200 feet deep, 

 and has ob\'iously originated in a fissure running west by south. 



