1869.] MURCHISON SUTHERLAND GOLD-FIELD. 315 



and limestones, which, thanks to the fossil discoveries of my friend 

 Mr. C. Peach, were proved to be of Lower-Silurian age. It was 

 also shown that these Lower Silurian rocks, in their extension east- 

 wards and dipping slightly to the east south-east, became more and 

 more crystalline as they trended in that direction, and that when 

 perforated by bosses of eruptive rocks, chiefly granite, they rolled 

 over in undulations in a highly metamorphosed condition, until they 

 were surmounted unconformably by the Old E-ed Sandstone and 

 younger deposits of the eastern coast. 



In order to be able to reason upon the probable sources of the gold 

 detritus which occurs in the gullies (valleys) of such hard crystalline 

 rocks of Eastern Sutherland, it is necessary to recur to those trans- 

 verse sections from W. to E. which I laid before this Society in 1858, 

 together with a geological sketch map * of the Highlands, in both of 

 which the true general order was first explained. 



In referring to these, a chief point which is to be borne in mind is 

 the peculiarity of the outline of the mountainous region of Sutherland 

 and Eoss, presenting a steep and rapid escarpment, down which the 

 waters cascade to the western shore, whilst they flow along a gentle 

 slope for many miles to the eastern shore. Thus the parting of the 

 waters in this region lies within four or five miles, and sometimes 

 less, from the western sea- shore, whilst it is from seventy to eighty 

 miles from the eastern shore, in which long descent the waters 

 flow over the metamorphosed Lower Silurian rocks, with occasional 

 bosses of granitic and other intrusive rocks. Now, however trans- 

 ported (probably by floods carrying great masses of ice, caused by 

 the melting of former glaciers — a view which, in a more extended 

 sense, has recently been applied by Mr. John Campbell, of Islayf, 

 who has examined the localities), it is evident that all the disinte- 

 grated materials of the great mass of the western and central High- 

 land rocks must have been transported eastwards. I am, indeed, led to 

 suggest that the gold debris found in the environs of Kil-Donnan and 

 Helmsdale are the result of the abrasion of extensive masses of the gra- 

 nitic and metamorphic Lower Silurian rocks which, occupying wild 

 interior tracts, extend eastwards to the district under consideration, 

 where their broken materials have been lodged in the depressions of 

 Eastern Sutherland. Eeasoning in this way, and looking to the 

 general character of the rocks between the west and east coast, I am 

 led to think that certain valleys on the long eastern slope of Eoss- 

 shire which accompany the line of Loch Shin and the river Oikel 

 may also be found to be slightly auriferous. It is here also to be 

 noted that the gold-bearing detritus of Sutherland occurs in a district 

 which exhibits in its environs the most striking evidence of granitic 

 eruption and of highly metamorphosed rocks. 



Thus on the Helmsdale shore we have the grand mountain-mass 

 of granite known as the Ord of Caithness, and on the north of 



* See Quart. Journ. Geol. Soc. vol. xv., Section, p. 360, and Map, pi. xii. ; 

 also vol. xvi. p. 215. 



t See "Something from the Gold-diggings in Sutherland," by the author oi 

 ' Frost and Fire,' from ' Odds and Ends,' No. 22. 



VOL. XXV. PART I. Z 



