144 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 



laccolite of the Cuillins, Isle of Skye, described and figured 

 by Harker.^"' 



A glance at Mr. Ball's map shoAvs a network of out- 

 crops Avhich at first are difficult to reconcile with the 

 conception of a laccolite. This network is not, however, 

 the outcrop of vertical and steeply dipping dykes striking 

 in every direction. It is the result of mapping more or less 

 continuous intrusions generally with a slight dip in a hilly 

 locality. Mr. Ball recognises this fact and writes : — ' ' In 

 many of the exposures the dyke walls dip at comparatively 

 low angles. In fact, most of the mapped loops are in reality 

 not due to branching of the dyke mass, but to partial 

 covering by schist islands or inliers."^' 



Away from the effect of the intrusions the Brisbane 

 schists strike N.N.W. and dip quite steeply to the E.N.E. 

 In discussing the Brisbane schists in the locality in cpiestion, 

 Mr. Ball states : — ' ' The strata have been much disturbed, 

 notwithstanding that steep dips are exceptional here about. 

 Even on the flat arches there has been much crenulation 

 and puckering." 



The expression "flat arches" fits in precisely with the 

 author's view as to the laccolitic origin of these low dips. 



To rpiote Mr. Ball further: — "The brecciation of the 

 schists along the faults on Finney's Hill is a puzzling 

 feature. The structure is certainly not due to compressive 

 forces. To explain it we must assume an arching of the 

 strata above a plutonic or hypabyssal intrusion sufficient 

 to cause a breaking-down of the beds under the tensile 

 stresses induced. Alternatively these stresses may have 

 been induced in the sedimentaries by a partial retrograde 

 movement (a sucking back, as it were) of the molten 

 magma." The author feels sure the great majority of 

 geologists would favour the former as being the more 

 probable hypothesis. The arching of the strata which Mr. 

 Ball "must assume" is the arching which I firmly believe 

 to exist. 



We have, then, found all the essential features of 

 irregular laccolitic intrusion, with the exception of the flat 

 bases. No evidence is available either way on this point at 



16 < < rpjjg Tertiary Ingeous Eocks of Skye, ' ' Mem. Geol. Surv. U.K. 

 1904, 85 et seq., fig. 15. 

 " Op. cit. p. 266. 



