1859.] mukchison — nokth highlands. 231 



between the upper limestone and the overlying so-called " gneiss " 

 or mica-schist, it is interstratified with the latter rock, and, being 



Fig. 9. — Section of the Junction of the Quartz-rock and Gneissose 

 beds above Eriboll House. 



1. Quartz-rock. 



2. Upper limestone. 



3. Gneissose quartz-rock. 



4. Gneissic strata. 



5. Felstone (granitic). 



6. Gneissic and micaceous schists. 



a part of the overlying deposit, cannot be cited in any sense as 

 forming a barrier between the quartzose calcareous group and the 

 superior strata. " w 



In the sequel it will be seen that, in following these beds on their 

 strike to Whiten Head, where the whole of the interstratified lime- 

 stone thins out, the granitic felstones really perform the part of 

 intrusive rocks which have been injected into the overhung schists 

 and dark green chloritic flagstones, although the regular order of 

 superposition of the latter is still undisturbed. 



In short, the observer who walks along the summits of the escarp- 

 ments above the House of Eriboll will see that all the flaggy, mica- 

 ceous or quartzo-gneissose series, with its siliceous flagstones, clearly 

 surmounts all the quartzo-calcareous series, and dips away gradually 

 to the E.S.E. Passing under the base of the lofty mountain of Ben 

 Hope (fig. 7), these rocks constitute indisputably a higher member 

 of the Lower Silurian series than the quartz-rocks and limestones 

 of Durness and Eriboll. These sections, I affirm, are as clearly 

 demonstrative of an ascending order as any which ever fell under 

 my notice or that of Professors Ramsay and Harkness ; and every 

 traveller who proceeds from Eriboll to Altnaharrow is invited to 

 witness the proofs of this order without even quitting the sides of 

 the high road. 



It is needless to ask such observer to contrast the old gneiss (a) 

 of Ben Spionnach or Rispond, distanl b few miles only, which dips 

 to the west-south-west, with any <>f these very different quartzose, 

 micaceous, or gneissose flagstones (d) on the east side of Loch Eriboll, 

 which are inclined t>> the S.K.; because, as the latter exhibit no 

 reversal of the easterly dip, it is physically impossible that the 

 superposed strata ran be equivalents of the rock which lies beneath 



all the quart /.use series (<) and dips to the west. (See section, Bg. 7. 

 p. 226j and map. Q. J. <i. B. Vot xv. pi. 12.) 



In regard t" the mineral distinctions and demarcations which 



have been drawn in the geological map of Macculloch*, and in all 



succeeding maps, between that which lias been called "gneiss" and 

 certain associated micaceous, chloritic, talcose, and argillaceous 



Ifaooullooh'a map waa oonstraDted, olrieuj from hit own material*, after his 

 death. 



\'>l.. \\ I. | ! I.l !. 



