Revieics — A. Harker — Eocks of Sk//e. 557 



•end abruptly against otliers (such as granite and agglomerate), not 

 because the latter are of later date, but owing to the resistance they 

 offered to the passage of the dykes. Like many of the other 

 problems which have confronted Mr. Harker in this region, this 

 last observation is an important one and capable of wide application ; 

 for, as he suggests, it may lead to a reconsideration of the age 

 attributed to certain intrusions which intersect the Carboniferous 

 and older strata in parts of England and Wales. 



The memoir is confined principally to the area mapped in detail 

 by Mr. Harker during the years 1895-1901, comprising the central 

 laccolitic masses of gabbro and granophyre and their surroundings, 

 the basaltic plateaux to the west and north-west, and some of the 

 islands off the east coast ; but the south-eastern part of the island, 

 which was surveyed by Mr. Clough, also receives consideration in 

 the descriptions of the minor intrusions in the older stratified rocks. 



After an introduction dealing chiefly with the general relations of 

 the volcanic series, the different rock-groups are treated as far as 

 possible in chronological order, and in each case descriptions are 

 iirst given of the field relations and then of the petrographical 

 characters. As regards the latter, Mr. Harker has been on the 

 whole merciful, and spared us too gi'eat detail ; in some cases an 

 additional interest is given to the description of thin-slices by the 

 discussion of the chemical analyses, no less than sixteen of which 

 have been made for the purpose of the memoir by Dr. Pollard. 



Although the gabbro and granite masses have been deposed from 

 their position as ancient volcanic cores, yet the remains of vast 

 craters filled with agglomerates haye been detected in Skye. These 

 were the vents from which took place the explosive eruptions which 

 marked the earliest phase of igneous activitj'^ in the island. The 

 succeeding tranquil fissure-eruptions of basalt were also accompanied 

 and partly succeeded by paroxysmal eruptions of trachyte and 

 rhyolite. In comparison with the basalts, however, the pyroclastic 

 rocks and more acid lavas play but a very minor role. A fact with 

 respect to the basalts, which Mr. Harker considers has not been 

 hitherto sufficiently appreciated, is the extent to which their apparent 

 thickness has been increased by the intrusion of dolerite sills of 

 later date. The greater part of the alteration (with production 

 of amygdules) which characterises these basalt lavas is attributed 

 by the author, not to ordinary weathering, but to changes produced 

 in them soon after their eruption by the " action of water of volcanic 

 origin." In the subsequent contact-metamorphism by the gabbro 

 and granite it is these early formed amygdules which show the 

 most interesting effects, viz., a restoration of the minerals (felspar 

 and augite) from which the zeolites and chlorites were originally 

 derived. 



To the second or plutonic phase of igneous activity are due the 

 most picturesque features of the scenery of Skye. This phase 

 consisted in the intrusion of laccolitic masses first of ultra-basic 

 rocks, then of gabbro, and lastly of granite and granophyre. The 

 descriptions of the partial fusion and incorporations of the gabbro 



