126 Rev. A. Sedgwick and Mr. Murchison on Deposits contained hcticeen 



rate and red sandstone system on the western coasts of Ross-shire and Suther- 

 land. On this subject we are not aware that there is any difference of opinion 

 amon"- those who have studied the general structure of Scotland. It forms no 

 part of our object to describe the secondary deposits on the south-eastern 

 flank of the Grampian chain : and the history of the red sandstone and con- 

 o-lomerate series of tiie N.W. coasts has been written by Dr. M^^CulIoch with 

 so many excellent details, that little more will be necessary for us than to refer 

 to his narrative ; adding, however, such observations as may seem to connect 

 it with the statements which we are about to offer. 



The greater part of the subsequent details will therefore be devoted to a de- 

 scription of the secondary formations which appear on the shores of the Murray 

 Firth, and occupy nearly the whole of Caithness. We commence with an ac- 

 count of the range of the old red conglomerates which rest immediately on the 

 primary rocks, and stretch in one nearly continuous mass through these exten- 

 sive tracts of country ; for their range when once ascertained, not only gives 

 us abase line to which all transverse sections may be afterwards referred, but 

 at the same time gives us a good approximation to the superficial extent of the 

 deposits which are included between this base line and the coast. 



We wish it were in our power at once to exhibit in a connected point of 

 view the several deposits of Caithness and the Murray Firth, which are built 

 upon the base of these old conglomerates. This task, however, we are not 

 able to accomplish ; and we are compelled to arrive at the conclusions we 

 wish to establish through the intervention of many distinct natural sections. 

 We, therefore, in the next place proceed to examine the sections on the coasts 

 of Caithness*, and by their help we show that the secondary formations of the 

 county are divided into three great natural groups ; viz. the old red conglo- 

 merates and sandstone ; the group of bituminous schist and siliceous flagstone ; 

 and the upper red sandstone. We then describe in considerable detail two 

 transverse sections through the deposits which are based upon the old red 

 conglomerates on the north-western and south-eastern shores of the Murray 

 Firth ; and, by a comparison of the several sections, have endeavoured to 

 identify the upper portion of these secondary deposits with those of Caithness. 

 Lastly, we consider the analogies presented by the red sandstone series on the 

 north-west coasts of Ross-shire and Sutherland. This manner of treating the 

 subject necessarily leads us into some repetitions, and into details which may 

 be tedious, but are, we think, unavoidable. It has, however, the great advan- 

 tage of separating matters of fact from all hypothesis, and of exhibiting the 

 phaenomena nearly in the order in which they must present themselves to any 



* See Plate XIV. 



