Vol. 60.] IGNEOUS ROCKS AT SPRING COVE. 161 



crystals, "with no definite outlines or cleavage. With this change 

 • omes in much reddish-brown colouring-matter, occurring in 

 irregular veins and fissures. In places the brown substance shows 

 distinct rhombohedra. sometimes with curved faces and projecting 

 into the vein, which is filled up with clear secondary calcite. 

 This brown substance, which is bright yellow and red by reflected 

 light, is doubtless carbonate of iron, carried down by percolating 

 waters from the basalt above, deposited in the limestone as chalybite, 

 and subsequently oxidized, giving to the limestone its pronounced 

 red tint, more especially for the first few feet below the junction. 



[28] Another junction- specimen is a reddish-brown rock, with 

 the appearance of a breccia in the hand-specimen. Under the 

 microscope, the basalt can be seen penetrating and absorbing the 

 limestone. The contact has evidently much affected both rocks. 

 The basalt is represented at the actual junction by a host of minute, 

 pale-green or nearly colourless needles (*? tremolite), which are 

 largely masked by iron-oxide. These needles are associated with 

 some brown and yellow glass and much secondary calcite, forming 

 a fine groundmass. The limestone is reddish-brown, structureless, 

 and polarizes faintly. 



24] Another junction-specimen is intensely red, and shows 

 under the microscope the ' ghosts ' of the original oolitic grains. 



[21] A slice from a specimen taken 3 feet below the junction 

 shows, besides the usual reddish-brown ferruginous matter in the 

 spaces between the oolitic grains, which in places has a marked 

 superficial resemblance to fragments of palagonitized glass, a large 

 number of nearly colourless rhombs of dolomite, fringing cavities or 

 veins filled with water-clear calcite. 



[23] A sample taken 8 feet below the junction, of a reddish- 

 purple colour, effervesces strongly with acid, and has a very tuff-like 

 appearance. Under the microscope it shows angular and rounded 

 fragments of oolitic limestone in a dark reddish-brown matrix, and 

 the borders of the fragments are strongly marked with the same 

 colouring-matter. But even here no certain igneous material was 

 detected, although it is possible that the highly-coloured matrix is 

 fine volcanic dust, and not colouring-matter brought down in 

 solution from the overlying basalt. 



IV. Relation of the Basalt to the Limestone above it. 



The determination of the precise nature of this junction is 

 obviously important, as bearing on the contemporaneity or intrusion 

 of the basalt. In the Survey account referred to above it is stated 

 (p. 106) that 



' flue volcanic dust appears in the overlying limestone for about 3 feet above the 

 surface of the lava, and thereafter the calcareous rock assumes its usual highlv- 

 •ossiliferous character/ 



I have cut and examined sections at and near the junction and for 

 about a foot above it, and can confirm the above observation. At 

 the actual junction, and for about a foot from it, lapilli of basalt, one- 

 Q.J.G.S. No* 238. M 



