1852.] SHARPE ON aUARTZ ROCK. 125 



either at the base of the Old Red Sandstone or at the base of the 

 Quartz- rock ; since this indication will materially assist them in their 

 search for this useful rock. Every calcareous deposit of any import- 

 ance which I visited belonged to one or other of those positions. 

 Some of the limestones of Banffshire may perhaps be exceptions, as 

 are also the limestones of the Oolites and Lias on some parts of the 

 coast. But, throughout the greater part of the Highlands, the only 

 limestone beds really worth working occur a little above the base of the 

 Old Red Sandstone and Quartz-rock, and these, like the calcareous 

 beds of the Old Red Sandstone elsewhere, are not continuous, but 

 occur here and there at about the same geological level. 



There are also some very insignificant masses of limestone in the 

 Gneiss and Mica-schist, but these are rare and of little value. The 

 limestone occurs, as one of the constituents of the foliated rock, in 

 sheets, rarely exceeding six inches in thickness, which are conform- 

 able to the folia of quartz, mica, &c., of which the rock may be com- 

 posed, and exhibit no internal traces of stratification. In a country 

 where limestone is so rare, it may be desirable to map these deposits 

 on economical grounds ; but geologically they have no more claim to 

 figure separately on our maps than have the quartz, mica, or felspar 

 which occur with them. An instance of limestone occurring in this 

 manner in mica- schist may be seen near Lawers, on the north side of 

 Loch Tay ; and in gneiss, in several spots on the north side of Loch 

 Maree in Ross-shire, especially in the hill behind Letter Ew ; and 

 other instances are probably to be found elsewhere*. 



I have endeavoured to show in the preceding remarks that the 

 quartz-rock of the Highlands must be divided between two most 

 distinct classes of rocks : — 



1 St. A foliated rock, allied to gneiss, with which it may be classified 

 without requiring a separate colour on our maps, or a distinct name 

 in our nomenclature. 



2nd. A stratified rock of sedimentary origin, altered from sandstone 

 into more or less homogeneous quartz-rock by plutonic action, as in 

 the now well-understood cases of the Stiper Stones and the Lickey. 



In considering to what formation of sandstone we are to refer the 

 metamorphic quartz-rocks, we must recollect that as yet we know of 

 no sandstone in any part of the Highlands older than the Old Red 

 Sandstone ; that this formation is more than equal in thickness to 

 the quartz-rock, and that the more modern sandstones play an insig- 

 nificant part in those districts, having only been observed at a few 

 places on the coast. It seems, therefore, reasonable to refer the 

 whole of the Quartz-rock to the Old Red Sandstone, especially as the 

 quartz-rock of Sutherland and Ross-shire undoubtedly belongs to that 

 formation, and the similarity of character and the frequent occurrence 

 of limestone in the same part of the series are strong arguments for 

 connecting all the stratified quartz-rocks together. The change in 



* I must warn the traveller in the Highlands that the pubUsher of MacCuUoch's 

 Map has most unfortunately chosen almost the same tints for " primary limestone " 

 and " trap-rocks and porphyry," so that, when in search of a supposed band of 

 limestone, he will sometimes come upon a trap-dyke. 



