Vol. 51.] MR. H. W. M0NCKT0N ON THE STIRLING DOLERITE. 487 



There are some interesting sections in the burns which rise 

 in the Glacial deposits and flow in an easterly direction. I will 

 take first the burn south of the house at Sauchieburn (see sketch- 

 map facing this page). It rises above the 700-feet contour, but 

 there are no exposures of rock above a level of about 570 feet. A 

 short distance north of the burn, at the point 5 on the sketch-map, 

 there is the rock with the peculiar magnetic characteristics which 

 has been already described. 



At the point 7 there is fairly coarse dolerite, and close to it the 

 burn falls over the cliff. At the bottom of the waterfall the rock is 

 fine-grained, and is underlain by an indurated altered sandstone of 

 a light colour which might perhaps be called a quartzite. 



At the point 8 on the sketch-map there is more igneous rock in the 

 burn. It rests against the stratified beds, and is no doubt a small 

 offshoot from the main mass of intrusive igneous rock. It is of 

 the fine-grained type, almost porphyritic, with minute rods and 

 hairs of iron oxide in bundles here and there. The porphyritic 

 felspars, which sometimes attain a length of 0*02 inch, are almost 

 wholly replaced by alteration-products. The rock is full of 

 carbonates in minute specks, and effervesces freely with acid. No 

 doubt these are marginal characters, and the rock, if worked into, 

 would probably turn out to be a dolerite. 



Resting against this igneous rock is a brown shale, and below 

 the shale a bed of limestone, probably one of Hosie's seams, as 

 indicated on the sketch-map. 



The limestone has undergone alteration and is dolomitic in places, 

 and does not always effervesce with cold hydrochloric acid. It is 

 extremely hard and contains a great deal of pyrite. 



Under the microscope, using a fairly low power, it is seen to be 

 crowded with small specks of hexagonal or roundish shape, and 

 about O02 inch in diameter. They are white by reflected light, 

 and seem to be isotropic. Under an ^-inch objective some of them 

 are seen to have a distinct radiating structure around a central 

 nucleus. This is shown in fig. 3, p. 488. 



Patches of iron oxide occur in this limestone and partake to a 

 certain extent of the form of some of the patches of iron oxide in 

 the marginal part of the igneous rock, with similar hair-like pro- 

 jections and minute rods. 



At the point marked 9 on the sketch-map, a few yards north 

 of the burn, we find a third occurrence of igneous rock just above 

 the 300-feet contour. It is the projecting part of the lowest ridge 

 described above. 



At the point marked 6 in this ridge I saw, in 1893, a section 

 showing the top of this igneous rock and its junction with the 

 overlying shale. The shale is white and much altered. The upper 

 part of tho igneous rock is of a dark blue colour, with a yellowish 

 band near the top. The top does not effervesce on treatment with 

 acid, but effervescence begins 0*40 inch down, and still lower there 



