680 REPORT— 1901. 



the Triassic sandstones rest partly on the Old Red Sandstone, partly on the Cat' 

 honiferous Limestone Series and partly on the Goal-measures. 



In 1878 appeared the third of Professor Judd's great papers on the Secondary 

 Eocks of Scotland, wherein he unraTelled the history of these strata as developed 

 in the east of Scotland and in the West Highlands. His admirable researches, in 

 continuation of the work done by Bryce, Tate, and others embraced the identifica^ 

 tion ot the life-zones, their correlation with those of other regions, the history of 

 the physical conditions which prevailed in Scotland during Mesozoic time, and the 

 working out of the structural relations of the strata.' He showed that their 

 preservation on the east of Scotland was due to the existence of great faults, and 

 those in the West Highlands to the copious outpouring of the Tertiary lavas. He 

 wns the first to detect the occurrence of Cretaceous rocks in the West Highlands 

 and to show the marked unconform ability which separates them from the Jurassic 

 strata. Plis main life-zones and his main conclusions regarding the Secondary 

 Rocks of Scotland have so far been confirmed by the detailed mapping of the 

 Geological Survey. An interesting addition to our knowledge of these rocks AVas 

 made by my colleague, Mr. Woodward, in the course of his field work, who found 

 the oolitic iron ore in the Middle Lias of Raasay, the position of which corresponds 

 approximately with that of the Cleveland ironstone.- 



The extensive plateau of Tertiary volcanic rocks in the Inner Hebrides has been 

 a favourite field of research ever since the time of Macculloch, the great pioneer 

 in West Highland geology. During the period under review much work has been 

 done in that domain. According to Professor Judd, that region contains the 

 relics of five great extinct volcanoes and several minor cones, indicating three 

 periods of igneous activity. The first was characterised by the discharge of acid 

 lavas and ashes, the molten material consolidating down below as granite ; the 

 second by the outburst of basic lavas, now forming the basaltic plateau, connected 

 with deep-seated masses that appear now as gabbi'O and dolerite ; the third by the 

 appearance of sporadic cones, from which issued minor streams of lava. ' 



In 1888 Sir A. Geikie communicated his elaborate monograph on the history 

 of Tertiary volcanic action in Britain to the Royal Society of ]"',diuburgh,' which 

 has been incorporated, with fuller details, in his recent work on 'The Ancient 

 Volcanoes of Great Britain.' His main conclusions may thus be briefly stated : 

 1. The great basaltic plateaux did not emanate from central volcanoes, but are 

 probably due to fissure eruptions ; 2, the basaltic lavas were subsequently 

 pierced by laccolitic masses of gabbi'o, which produced a certain amount of contact 

 alteration on the pre^•iously erupted lavas ; 3, the protrusion of masses of grano- 

 phyre and other acid materials by means of which the basic rocks were disrupted. 



During the last six years Mr. Harker has been engaged in mapping the central 

 part of the isle of Skye, and in the petrographical study of the rocks, the results 

 of which have been summarised in the annual reports of the Geological Survey. As 

 regards the basaltic lavas, he finds that while they have been of vast e.xtent the 

 individual flows have been of feeble volume, and show no evident relation to 

 definite centres of eruption. There were two local episodes, however, which took 

 the form of central eruptions : one represented by a number of explosive outbursts 

 at certain points ; the other, in the basalt succession, gave rise to rhyolitic rocks. 



Mr. Harker further finds that the succeeding plutonic phase of activity, confined 

 in Skye to what is now the central mountain tract, is represented by three groups 

 of plutonic intrusions, in the following order : peridotites, gabbros, and granites. 

 The metamorphism set up in the basaltic lavas near the large plutonic masses pre- 

 sents points of interest, especially the widespread formation of new lime-soda- 

 felspars from the zeolites in the lavas. 



After the intrusion of the granite of the Red Hills, Mr. Harker finds that 

 igneous activity took the form of intrusions of smaller volume, but in some cases 



' Quart. Journ. Gcol. Soe., vol. xxix. p. 97, vol. xxsiv. p. G60. 



= Geol. Mag., Dec. 3, vol. x. p. 493 (1893). 



' Quart. Journ. Gcol. Sac, vol. xsx. p. 220. 



' Trans. Boy. Sac. Edin., vol. xxxv., part 2, p. 23. 



