Geological Society of London. 329 



versing gneissose beds. In the two streams last mentioned, and in 

 all the other tributaries of the river Ullie from the north, the dip of 

 the flaggy quartzose and gneissose rocks through which they run is 

 easterly, with a few local rolls ; till at Cill-Pheader burn, 3^ miles 

 from Helmsdale, the porphyritic rock of the Ord is reached, and 

 continues to the coast, and the drift is no longer worth washing. 

 Within the neighbouring district of Caithness, the metamorphosed 

 Lower Silurian rocks appear as quartzite Mountains, some of which 

 are capped uncomformably by Old Eed Sandstone. Where flaggy 

 gneissose beds occur, as at Allt-an-lic, the easterly dip is distinct, 

 and persists up to the junction with the Devonian Sandstones on the 

 S.E, These latter, at Berriedale, on the coast, dip E. and N.E., 

 passing under the bituminous flags, which principally represent this 

 system in Caithness. 



If the gold of Sutherland be derived from the binary compound of 

 felspar and quartz (c), so abundant in Suisgill and Cill-Donnan, 

 the Caithness district does not promise to be richly auriferous ; as 

 this rock is, so far as could be seen, by no means j)lentiful there. 

 Judging from the frequency with which this quartzo-felspathic rock 

 is associated with the richest washings, and from the fact that 

 gold has been found in small rolled specimens of stone which seem 

 to have been derived from this rock, it is possible that it may yet be 

 discovered to be the matrix of the gold. Hitherto, however, none 

 Las been found in rock in situ. 



It is believed that the extent of the gold-fields will be determined 

 by the range of the metamorphosed Lower Silurian rocks, and that 

 its richness may, therefore, be in proportion to the degree in which 

 it is associated with such rocks as are either eruptive, or highly 

 metamorphosed. 



The connexion of the Pictish Towers with this subject is worthy 

 of notice. Of 60 of these forts in the county of Sutherland, 33 occur 

 within the Cill-Donnan district. They seem to have been erected 

 against maritime invaders, who were probably attracted by the 

 known existence of native gold. The very numerous sepulchral 

 tumuli of the auriferous district imply a large archaic population. 



Discussion. — Prof. Ramsay regarded it as certain that no quantity of gold would 

 ever be found in purely glacial deposits, as in such detritus specific gravity went for 

 nothing ; but when those deposits came to be sorted by water, the gold became ap- 

 parent, as in this case. He agreed with the author in regarding the granites in 

 Kildouan Burn as metamorphic rather than intrusive, and had long held this opinion. 

 The felspathic dykes were probably due to other causes. 



Mr. D. Foi-bes, on the contrary, regarded the granite as eruptive, and accounted 

 for the granitic veins following the lines of stratification, inasmuch as those were the 

 lines of least resistance. The smaller insterstices caused by the intrusion of the granite 

 would be filled with quartz veins derived from the granite, both probably containing 

 gold. He considered that the gold had not been derived from Silmian rocks, but 

 from the intruded granite, or from the quartz veins. 



The author was inclined to regard the granite in some instances as intrusive, and 

 in others as metamorphic. 



2, " Observations on the ' Nuggetty Eeef,' Mount Tarrangower 

 Gold-field." By Dr. G. H. F. Ulrich, F.G.S. 

 The author commenced by indicating the positions and characters 



