138 MR. J. MORinsON ox [vol. lxxiv r 



are absent, and the sills appear to have been intruded on planes of 

 weakness rather than disturbed by subsequent movement. Certain 

 dykes in the west present features not common to the lampro- 

 phyres generally ; but these may confidently be referred to the 

 same magma, as similar features are occasionally reproduced in 

 the mixed series. An acid sill intruded in the volcanic rocks north 

 of the granite shows some resemblance in the field to the Ordovician 

 sills of other parts of the Lake District ; but sufficient reasons do 

 not appear for separating it from somewhat similar rocks which 

 undoubtedly belong to the granite. Everything points to the 

 same conclusion, that the whole of the minor intrusions 

 of the area are connected directly or indirectly with 

 the same magma. 



The general age having been fixed, it remains to enquire as to the 

 order in which the various intrusions played their part. Conclusive 

 evidence, such as the cutting of one set by another, is unfortunately 

 rare ; but sufficient can be gathered from the few instances that 

 occur to enable one to form a fairly definite idea as to the 

 sequence in which the great groups were intruded. 



Intersecting dykes are very rare. Far down the Stakeley Valley 

 two dykes are seen close together in the bank of the stream, one 

 belonging to the mixed series, the other an acid intrusion of the 

 ordinary type. They approach each other, but are lost in mid- 

 stream. The marginal portion of the basic dyke ends abruptly 

 against the grit, and appears to be moved aside by the acid dyke, 

 which, however, is so decomposed that it disappears from view 

 before meeting the other. In the adjoining area lamprophyres 

 occasionally cut the felsite sills. The latter, there very abundant, 

 are unlike any of the acid intrusions near the granite, and their 

 exact position in the sequence is perhaps a matter of doubt. 



The granite is cut by acid veins of fine aplitic character belong- 

 ing to a late stage of activity and traversing granite and basic 

 patch indiscriminately ; but careful search has failed to reveal its 

 penetration either by basic or even by mixed dykes. This, however, 

 is not conclusive evidence. The reluctance of basic dykes to enter 

 certain formations is well known, and instances need not be quoted. 1 

 The fact that granite is rarely pierced lrv basic intrusions has to 

 be taken into account. 



Occasionally dykes have been intruded along planes which served 

 as channels for previous magmatic flows. Although rare, these 

 are of importance in determining the true sequence. An intrusion 

 of this kind occurs near Gill Farm. The centre is a quartz-felsite 

 containing large Carlsbad twins of pink orthoclase. The mar- 

 ginal rock is a modified lamprophyre of the mixed series, with 

 the usual orthoclase- and quartz-xenocrysts in a biotite-studded 

 ground-mass of the type previously mentioned as resembling the 

 minettes. The junction of the two rocks is marked by a small 

 belt of mixed material, 12 inches wide, comprising numerous blocks 



1 ' The Tertiary Igneous Eocks of Skye' Mem. Geol. Surv. 1904, p. 432. 



