﻿304 



ME. TT. "B. WEIGHT OX THE 



[May 1908, 



and sheets throughout the islands is oue of remarkable significance. 

 Their number increases rapidlj' as we pass from the area of slight 



to that of intense secondary 



Pig. 6. — LampropTiyre dyke on the 

 shore north of Port an Ohain, 

 northern end of Colonsay, in- 

 truded along the cleavage of the 

 jprimary movement^ and involved 

 in the folding of the secondary 

 move^nent. 



moTement. Thus in Zone 1 

 (fig. 2, p. 301) we scarcely 

 ever see a lamprophyre show- 

 ing even incipient cleavage. 

 In Zone 2 they are to be found, 

 but are neither strikingl)' 

 cleaved nor abundant. .In 

 Zone 3 even the larger and 

 more massive dykes have 

 suffered, and the smaller ones 

 are often remarkably folded 

 and cleaved. In Zone 4 they 

 are reduced to a schistose 

 state, and do not strike one 

 at first glance as markedly 

 different from the adjoining 

 phyllites. 



It will, perhaps, be conceded 

 '^ that we have in the intrusion 



of this series of dykes a fair 

 indication of a very considerable lapse of time between the two 

 movements. It has been found possible, however, to go even 

 further than this. 



y. The Relation oe the EAETH-MovEiiEXTs to the 

 Plutonic Masses. 



A careful examination of the syenite to the north of Xiloran Bay 

 has thrown considerable light on the question. The remarkable 

 breccia occurring along the margins of the plutonic mass, and 

 referred to above, contains abundant fragments of the adjoining 

 Torridon sediments, exhibiting clearly the primary cleavage and 

 lying at all angles to one another. They plainly had this cleavage 

 impressed upon them before their inclusion in the breccia, which 

 must therefore have been formed at a period subsequent to the first 

 movement. The syenite, which contains caught-up fragments of 

 the breccia, cannot be earlier than it ; and it is, therefore, quite 

 safe to conclude that both syenite and breccia are distinctly later 

 than the first movement. 



Evidence of the relation of the syenite and breccia to the 

 secondary movement is also forthcoming. They are traversed by 

 several dykes which have been affected by this movement. The 

 most remarkable of these is to be seen cutting the syenite on Eilean 

 Easdale. It is about 3| feet wide and has a general trend about 

 jS". 10° E., but takes a decided double bend about the middle of its 

 course. A band about a foot wide on the east side of the dyke is 

 rather fine-grained, but the rest is coarser. There are, besides, very 



