76 



HA RD WICKE 'S S CIE NCE- G SSI P. 



istic rhombohedral cleavage, whilst in the dolomitised 

 portion the curved or "saddleback" crystals were 

 equally well developed. The prevailing form was as 

 shewn in Fig. 41, which is often most distinctly recog- 

 nised in the variety of dolomite known as pearl spar, 

 but occasional groupings were found in the form 

 indicated by Fig. 42. 



Isolated portions of the dolomite afforded some 

 very interesting metallic characters. Emerald green 

 patches abundantly scattered over the surface seemed 

 to indicate the presence of carbonate of copper 

 (afterwards proved by analysis) ; and smaller spots of 

 a blood-red colour more sparsely distributed, ap- 

 peared to denote the oxide of the same metal ; but 

 owing to their position on the surface, this could not 

 be verified without damaging the specimen more or 

 less. The prevailing colour of the specimens being 

 light brown inclining to ochre, suggested the presence 

 of sesqui-oxide of iron, and that this existed in large 

 quantity was proved by the strong yellow colour of 



line, but some miles nearer to town, is another 

 locality known as Killester, where there is a small 

 exposure of the limestone formation laid bare in 

 making the cutting, and now occasionally used as a 

 quarry. The strata are immediately overlaid by a 

 boulder clay, the stones of which have a markedly 

 rounded form, and are scored with deep striae, giving, 

 it is believed, strong evidence of glacial action in the 

 neighbourhood. The stone in general is of a shaly 

 character, though there are some good beds. They 

 are intersected at intervals by numerous vertical 

 joints, all highly mineralised, the crystals of carbonate 

 of lime being very well developed. The prevailing 

 form was the following combination of the hexagonal 

 prism with rhombohedrons (Fig. 43), some of the 

 crystals reaching a length of from two to three inches. 

 Scalenohedrons were also abundant, but not nearly 

 so large in size. The crystalline forms of calcite 

 being very numerous, other combinations of the 

 prism and rhombohedron, &c., occurred, but not 



Fig. 41. 



Fig 



42. 



the solution, when a portion was afterwards pul- 

 verised and dissolved in hydrochloric acid ; a dark 

 coloured mass resulted from this, which, on being 

 heated under the blowpipe, became magnetic. 



Perhaps the most interesting feature observed was 

 a series of dendritic marks on some of the specimens 

 obtained, a few being not inferior in elegance to the 

 delicate tracery observed on moss agates, and some 

 of the finer sandstones. These are now well known 

 to be caused by infiltration of the metals iron or 

 manganese when in a state of solution, and that the 

 latter was probably the agent, appeared by the man- 

 ganese reaction being very decidedly given when a 

 small portion was tested^ in' the usual way with car- 

 bonate of soda on platinum foil. Iron, however, 

 existed in such quantity in every specimen tested, 

 that it was impossible to say it had no part in con- 

 tributing to the forms mentioned. 



Many other points of interest were also noted on 

 that occasion, but space will not allow of their being 

 dwelt on further at present. On the same railway 



Fig. 43. 



with the same frequency. It was curious, however> 

 to note an occasional single crystal of quartz standing 

 amid the calcite, often so closely resembling it in 

 form and translucency as to render it no easy matter 

 to distinguish the difference until the unerring test of 

 hardness was applied by the penknife. A large heap 

 of broken stone and shale was in a corner of the 

 quarry, and on turning over some of the crystalline 

 surfaces, copper pyrites were found freely distributed, 

 evidenced by their yellow colour, sphenoidal crystals 

 of the tetragonal system, and the comparative ease 

 with which they yielded to the knife. Bitter spar 

 was equally abundant in much the same positions. 

 In fact, throughout the whole district I have men- 

 tioned, dolomitised limestone, accompanied by 

 copper pyrites, is a prominent feature. 



Perceiving something to glisten slic;htly in a bed of 

 shale, I proceeded to dig it out with my cold chisel, 

 which I succeeded in doing with a little trouble. 

 On looking at the lump more closely, I saw that it 

 had the peculiar pale brassy colour of iron pyrites, 



