140 Rev. A. Sedgwick and Mr. Murchison on Deposits contained between 



enormous crumbling dislocated masses of red marl and sandstone, containing 

 a few bands of bluish flagstone which resemble the Caithness schist. These 

 masses o-radually pass into a strong red sandstone like that of Trefad, and ex- 

 tend towards the headland of the Ord. They are not, however, brought into 

 contact with it, but are cut off from it by a mass of highly inclined conglo- 

 merate forming a lofty cliff, which terminates against the granite. The junc- 

 tion is nearly marked by a cascade of the Ousedale rivulet, which tumbles from 

 the height of about 100 feet over these conglomerates into the sea. We here 

 observe a somewhat startling pha^nomenon, which we do not however believe 

 to be of unfrequent occurrence. A part of the conglomerate is so perfectly 

 granitoid, that neither by hand specimens, nor even by an examination of the 

 sections in the cliiT, is it easy to determine where the depository mass endSj 

 and tlie crystalline rock begins. What was the exact state of the granite at 

 the time the formation of the old conglomerate commenced, it is not perhaps 

 necessary to inquire ; but it is evident that mechanical agents by some means 

 or other produced a separation (almost without any fracture) of the crystalline 

 constituents of tiie rock. In this way was produced a granitic sand composed 

 of nearly unbroken crystals of quartz, felspar, and mica^ which, on being re- 

 cemented, produced that portion of the conglomerate rocks we are here de- 

 scribing. They do not, however, extend far from the granite, but soon begin 

 to present a coarser texture, and pass into a well-marked mechanical rock. 



With these conglomerates terminates the whole Caithness secondary system, 

 being here cut ofl" by the granite of the Ord, which, after forming a bold head- 

 land for about two miles, is brought into contact with^ and has brecciated a 

 great mass of, the oolitic series*. 



It appears, therefore, that the secondary deposits of Caithness may be di- 

 vided into three great natural groups. 1st. The old conglomerates which 

 contain some subordinate masses of red sandstone, flagstone, and red marl, 

 and which, through the intervention of thin beds of red sandstone, sometimes 

 graduate into the next system f. 2ndly. A great formation of alternating beds 

 of siliceous and calcareo-siliceous flagstone; dark, foliated, bituminous lime- 



* The description in the text plainly shows that the granite of the Ord must have existed prior 

 to the formation of the old conglomerates. This fact does not, however, prove that it then 

 existed at its present elevation ; nor, according to our view of the subject, does it in any way in- 

 validate the hypothesis which considers the brecciated structure of the oolite to have originated 

 in the last elevation of the primary crystalline masses of the Ord. (Sec Geol. Trans. Second 

 Series, vol. ii. Part II. p. 307, &c.) 



t The sandstones of this part of the series are not always of a red colour. At Port Skerry the 

 conglomerates (which are, however, in a very degenerated form) graduate through the interven- 

 tion of brown and greyish sandstone into the upper system. 



