1873.] JTJDB — THE SECONDARY BOCKS OF SCOTLAND. 115 



of some of them (that extraordinary phenomenon which has justly 

 excited the wonder and severely taxed the ingenuity of Murchison 

 and other geologists who have examined and attempted to account 

 for it) might be due to the breaking-up and redeposition of some of 

 the beds*. 



I shall now proceed to describe the facts which I have been able 

 to observe concerning the position of tbe Jurassic strata, and their 

 relations to the Palaeozoic rocks, and then indicate the conclusions 

 to which they point as to the circumstances of deposition and of the 

 subsequent disturbances of these strata. By this means I hope to 

 be able to demonstrate what were the remote causes which led to the 

 preservation of the interesting masses of Mesozoic strata to be de- 

 scribed in the present memoir. 



It will be convenient, in order to make the subject as clear as 

 possible, to describe a line of section passing across the centre of the 

 most important Jurassic area, where the rocks attain their greatest 

 development and present the most satisfactory exposures. Such a 

 line of section we have, as pointed out by Sir Roderick Murchison, 

 passing through Clyne and Brora, and crossing a breadth of upwards 

 of two miles of Secondary strata. When the main facts with regard 

 to this most important section have been established, it will only be 

 necessary to refer, in more general terms, to the various sections to 

 the north and south of it respectively which serve to illustrate the 

 relations of the Secondary to the Primary strata. 



§ 1. Description of the Section through Beinn-Smeorail, Clyne Kirk, 

 and Brora, N.W. to S.E. (fig. 1). 



The great series of metamorphic rocks which covers all the 

 central parts of Sutherland, have now, through the discovery of 

 fossils by Mr. C. Peach, and the study of the physical relations of 

 the beds by Sir Roderick Murchison and Professors Ramsay, Geikie, 

 and Harkness, been referred to the age of the Lower Silurian f. 

 These rocks, which have been very happily termed by Murchison 

 " altered flagstones," present the most varied characters, passing 

 from flaggy quartzites or altered sandstones, in which crystalline 

 minerals just begin to appear along the planes of stratification, up 

 to the most highly granitic gneiss, and perhaps into true granites. 

 The prevailing dip of these strata is towards the south-east ; and 

 they are usually inclined at very high angles, often greatly contorted, 

 and sometimes traversed by numerous veins of granite, quartz, fel- 

 spar, &c. As a rule they do not form striking elevations, and give 

 rise to but tame and monotonous scenery J. 



* "On the Geognosy of Sutherlandsbire," by R. J. H. Cunningham (1839), 

 p. 37, published in vol. xiii. of the ' Transactions of the Highland and Agricul- 

 tural Society of Scotland.' 



t Quart. Journ. Geol. Soc. vol. xiv. (1858) p. 501 ; vol. xv. (1859), p. 353 ; 

 vol. xvi. (I860), p. 215; vol. xvii. (1861), p. 171; vol. xvii. (1861), p. 256; 

 vol. xviii. (1862), p. 331. 



| These strata have been more particularly described by the Eev. J. M. Joass, 

 Quart. Journ. Geol. Soc. vol. xxv. (1869), p. 314. 



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