ALTERED LIMESTONE OF STEATH, BKTE. 67 



Another character by which the older is strongly contrasted with 

 the younger group of limestones is its much less distinctly marked 

 bedding. Along the shore-sections nothing can be more decided 

 than the division of the Liassic strata into layers varying from less 

 than an inch to two or three feet in thickness. Limestones of 

 varying texture and composition there alternate with each other, 

 and are sometimes separated by bands of dark micaceous shale. In 

 the limestone tract of the interior, however, no such alternations 

 are to be found. Thick solid masses of limestone occur there with 

 only faint marks of stratification and with no trace of any associated 

 micaceous shales. It is impossible to believe that such a contrast 

 can be explained by any process of welding or other alteration due 

 to the action of eruptive rocks. The limestones have been litho- 

 logically distinct from the beginning. But though the bedding is 

 far less conspicuous than it is among the gently inclined Liassic 

 strata of the shores, it may almost anywhere be detected in the 

 older limestone. It is traceable by bands of different colour and 

 texture, and conspicuously by the lines of dark cherts which run 

 parallel to each other like flints in the Chalk. Hence it is a 

 mistake to speak of this limestone as " unstratified." Its com- 

 ponent beds are for the most part placed at high angles of inclina- 

 tion, sometimes even on end, and the direction and amount of dip 

 vary continually within a short space. In these respects they offer 

 a striking contrast to the undisturbed Liassic strata that surround 

 them ; while, on the other hand, they present the closest resemblance 

 to the Lower Silurian limestone of Sutherland and Eoss. 



§ 2. Steatigraphical Chaeactees of the Limestone, 



Every observer who has rambled through the inland parts of the 

 district of Strath has noticed the remarkably disturbed condition of 

 the limestone just referred to. The beds rapidly change their angle 

 and direction of dip as one tries to follow them along the hill-sides, 

 until it may seem altogether hopeless to make out any recognizable 

 order of succession among them. Nevertheless I am convinced that 

 when they are attacked in full detail and traced upon maps of a 

 large scale, they will ultimately be reducible to order. The frequent 

 and sudden alterations in their inclination are precisely like those 

 that mark the outcrop of the Sutherland limestone where it comes 

 within the influence of the great thrust-planes of that region. In 

 Assynt, for example, the same group of rocks has been heaped up 

 and pushed forward to such an extent that a few hundred feet of 

 strata are repeated again and again in highly inclined or even 

 vertical positions and made to cover a breadth of several miles of 

 ground. So too in Strath, the great breadth of limestone and the 

 high dip of the beds do not probably indicate a considerable thickness 

 of rock, the same beds being constantly brought in again by thrusts, 

 faults, and folds. 



Until a detailed survey of the ground is made, any attempt to fix 

 the order of sequence among the various portions of the limestone 



f2 



