332 MK. G. BARSOTT OX THE OCCFKEElJsrCE OF [Aug. 19OI, 



The Jasper and Green-Rock Series. 



The highest known member of this series consists of rather fine- 

 grained sandstones, which, in a little stream near Brawliemuir, are 

 infolded with the originally underlying shale. They differ from 

 the Margie Grits, owing to the abundance of microcline in some 

 parts of them, which has not yet been detected in these grits. 

 Microcline is very rare in the Highland rocks near this locality, so 

 that these sandstones have probably had a less local origin than 

 the Margie Grits. This conclusion is strengthened by the nature 

 of the underlying grey slaty shale, which has always a deceptively 

 crystalline aspect. Thin microscopic sections of the latter rock 

 show that it is less crystalline than many shales of the Coal- 

 Measures : its finely crystalline aspect is due to the fact that it is 

 built up mainly of minute clastic micas, embedded in a matrix of 

 decomposed micaceous material, in which movement would take 

 place with great facility. The clastic micas are so extremely small 

 as to make it certain that the materials were laid down on the sea- 

 floor near the edge of the zone of sedimentation, or on an area where 

 deposition proceeded with extreme slowness. 



The probable deep-water origin of this grey shale is confirmed 

 by the fact that it overlies a bed of jasper, in which ray colleague 

 Mr. Peach detected circular bodies resembling the radiolaria in the 

 cherts of the Southern Uplands. Only at one place, however, have 

 radiolaria been detected in the jaspery chert, notwithstanding 

 its great development in this region. Though the jasper is rarely 

 sheared, it is usually much shattered, the lines of fracture being 

 filled with quartz, which is always more coarsely crystalline than 

 that in the jasper, and it is usually free from the iron-oxide 

 to which the colour of the jasper is due. In places the jasper 

 passes upward into a jaspery phyllite with a lower silica-per- 

 centage, and occasionally this phyllite appears to replace the 

 jasper. Being softer, the phyllite is almost always sheared. In 

 a few instances, however, even the jasper is ' milled,' as in the 

 little stream near Brawliemuir. Though the red jasper is the 

 type commonly met with in these areas, patches of green chert 

 appear about the North Esk, where they are seen to be part of one 

 and the same set of cherts, the difference in colour being due to the 

 comparative absence of iron-oxide. 



In several cases the silica-percentage of these cherts and jaspers 

 has been ascertained, the results being given below : — 



SiOg = 88-85. Typical red jasper, North Esk ; the most abundant type. 

 S1O2 = 71-50. Jaspery phyllite, North Esk ; fairly abundant in many 



localities. 

 SiO., = 93 30. Pale jasper, finely milled, Burn of Brawliemuir ; milling 



exceptional. 

 SiOa = 93-86. Muliion Island chert ; rarely if eyer sheai-ed. (Quoted 



for comparison.) 



The mode of occurrence of this jasper leaves no doubt as to its 

 sedimentary origin ; but the evidence that it was originally a radio- 



