14 ON THE AGEICULTURE OF THE COUNTY OF SUTHERLAND. 



the Primitive and Transition systems, tlie Primary rocks consist- 

 ing chiefly of coarse granite, gneiss, syenitic gneiss, and mica- 

 schist. Sir Humphrey Davy examined the east coast of the 

 county, and from his manuscript report, which is treasured in 

 Dunroliin Castle, lengthy extracts are given in the "New 

 Statistical Account of Scotland." He states that the Primary hills 

 in the neighbovirhood of Dunrobin are composed of felspar, 

 quartz, mica, and horneblende ; that the only veins he had seen 

 in the rocks were quartz, in which there were no indications of 

 metallic foundations ; and that the highest Secondary hills in 

 that district, extending in a line from Loch Brora to Strathfleet, 

 are composed of hard silicious sandstone and pudding stone, con- 

 taining large fragments of the Primary rocks. The Transition 

 rocks of Sutherland, he says, are not numerous nor wide-spread ; 

 but some of the hills in the immediate neighbourhood of Dun- 

 robin and Strathfleet, Ben Bhraggie, Ben Horn, and the Silver 

 Hill, for instance, are composed of red transition and breccia, the 

 sandstone being in some parts white, in some grey, and m others 

 iron-brown. The Secondary rocks, which he says are more interest- 

 ing, occupy but a small space, and are probably incumbent on 

 the red sandstone and breccia referred to. " The true Secondary 

 strata of the east coast of the county occupy an extent of G or 

 7 miles, filling up a sort of basm between the Transition hills in 

 the neighbourhood of Dunrobin and those in the parish of Loth. 

 The upper stratum is a sandstone of different degrees of hard- 

 ness and composed of silicious sand cemented by silicious matter. 

 Below this occurs an aluminous shale containing pyritous matter, 

 carbonaceous matter, the remains of marine animals, and of land 

 vegetables. Beneath this shale, or rather alternating with it, a 

 stratum occurs, contaming in some of its parts calcareous matter 

 and passing into limestone, but in general consisting of a silicious 

 sand agglutinated by calcareous cement. The coal-measures 

 occupy the lowest part of this Secondary district which has yet 

 been exposed. The hard sandstone is principally composed of 

 pure silicious earth. It is not acted upon by acids, and is not 

 liable to be decomposed by the action of air and water. The 

 shale contains no calcareous matter near its junction with the 

 coal. The limestones found m the Secondary strata contain no 

 magnesian earth, and are adulterated only with aluminous and 

 silicious earths and oxide of iron. They differ very much in 

 purity in different parts." Another writer says that gneiss com- 

 poses at least four-fifths of the whole surface of the county, and 

 that the Old Eed Sandstone occurs in patches both on the north- 

 west towards Cape Wrath, and on the south-east along the 

 Dornoch Firth. In the last portion he says it is succeeded by 

 one of the most remarkable geological formations in Scotland, 

 the Brora coalfield, in connection with which there are strata 



