330 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



east to west, greatly contorting the schists and reversing their dip. 

 Nearly parallel with this axis we have several bands of greenstone. 

 We may suppose then that a portion of the country on the north 

 side of this latter east and west line was elevated at the time of the 

 formation of the valley, along which the river runs to a somewhat 

 greater extent than that portion lying on the south side of the line, 

 and this was one stage of the uplifting of the Old red conglomerate. 



Another disturbance of a different date is however conspicuous 

 at the mouth of the river, between high and low water ; and^ a very 

 distinct line is drawn by the difference between the blue and claret- 

 coloured schists, which always immediately (though unconforma- 

 bly) underlie the Old red conglomerate. There is then exhibited 

 a line of principal fault running S. 40° W. magnetic, the rise 

 being on the north-western side; and a small ridge of limestone 

 runs out to sea in a direction S. 50° E., marking another fault at 

 right angles. 



It will be seen that these directions coincide with those which we 

 have been continually noticing in connexion with the series of 

 bosses ; and by the disturbance last alluded to, it will be clear that 

 the Old red conglomerate on the north-west or upcast side of the 

 fault received another elevation. 



I have not stated distinctly which series of disturbances happened 

 first, and this may perhaps be a matter for further consideration. 

 My own impression is, that the first elevation caused the fault run- 

 ning S. 40° W., since the line of demarcation between the blue and 

 claret-coloured schists, which were formed by the fault running 

 nearly south-west, appears to be broken by the other which crosses 

 it. A large quantity of sand and shingle unfortunately covers up 

 a portion of this line, and prevents a conclusive determination on 

 this point. 



Crossing the country now in a north-westerly direction, we may 

 trace conjecturally the line of outcrop of the Old red conglomerate, 

 although it is entirely covered up by diluvial drift or boulder clay 

 from the Brough to Ijeyond Ballasalla, where it appears in the little 

 stream which runs from St. Mark's and joins the Silverburn a little 

 above Crossag Bridge. It is also seen in the road above the umber 

 works. 



In this neighbourhood the conglomerate has entirely lost its red 

 colour in the upper beds, and is very thin, the quartz pebbles 

 being merely a white gravel in a limestone paste. Further on, at 

 Crag Mill, an elevation of the schist in a line crossing the Silver- 

 burn in a direction S. 80° W. has cut off the continuation of 

 the outcrop of the Old red conglomerate ; but following the stream 

 upwards for 300 yards across the bridge we come upon it again, 

 forming the ridge of a small semicircular basin in which the beds 

 are nearly horizontal. There is here an indication of our having 

 attained the original limit, in this direction, of the southern lime- 

 stone basin of the island. 



In passing up the Silverburn we have however been following a 

 line of fault running in a direction N. 10° W. magnetic. This 



