﻿238 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Feb. 20, 



distinction between tbe planes of cleavage and the lines of deposit* 

 as marked by tbe colour of tbe slates. But tbe parallelism of tbe 

 mica-scbist (a sandy quartzose micaceous rock) to the clay-slate 

 which succeeds, and to which Mr. Sharpe applies bis remarks, is 

 indeed one of the phenomena on which we have been all along in- 

 sisting, — viz. that these different mineral masses of the Highlands 

 succeed to each other regularly, and are fairty linked together, so as 

 to form one great series. 



In truth, if the observer follows any one mineral stratified mass 

 Upon the strike of the beds, he will often find that what at one ex- 

 tremity of it was highly crystalline is at the other much more earthy 

 and unaltered. Again, if he examines many of tbe quartzose, schistose, 

 and calcareous masses, he cannot fail to observe the essential cha- 

 racters of ordinary stratified sediments, such as way-boards dividing 

 different mineral substances, wavy surfaces, joints, and all the con- 

 comitant appearances, including occasional gritty and even pebbly 

 layers. 



In Mr. Sharpe's mapt there is one dominant feature which agrees 

 with our observations. He gives to the gneiss of the Lewis and 

 the western coasts of Sutherland and Ross a true north-westerly 

 and south-easterly strike, and thus exhibits it at right angles to the 

 strike of nearly all the other crystalbne rocks of tbe mainland. But, 

 never having observed tbe true order of superposition of the different 

 mineral masses in the north-west, which is the foundation of all our 

 induction, be follows Maccullocb and unites all these crystalbne rocks 

 in one gneissose and micaceous series, and treats all our lines of 

 stratification (and as such they were viewed by Hutton and also by 

 Maccullocb) as lines of " foliation." In fact, these so-called lines of 

 fobation, and the transverse sections of them which Mr. Sharpe exhi- 

 bits, may serve in a broad sense to represent our lines of stratification. 

 In his generalized and theoretical diagrams also, bis arches corre- 

 spond in a general way with the bnes of anticlinal axes ; with this 

 difference, however, that he does not insert, as the complement of 

 anticbnes, lines of syncbnal troughs J, which, as we have shown in the 

 previous memoir, do really exist. He has, moreover, omitted alto- 

 gether the bands of limestone, which are of such importance in demon- 

 strating the coincidence of stratification-planes and bnes of fobation, 

 and in working out tbe geological structure of the Scottish Highlands. 



No better illustration, indeed, of our own "views can be given than 

 by referring to Mr. Sharpe's own sections. First let us take bis 

 general sections, figs. 1 and 2, which in a traverse of ninety miles 

 across Scotland exhibit at least five great anticlinals, and all his lines 

 of fobation would be our bnes of deposit. Next, in fig. 3, the mica- 

 schist of Ben Lomond (chloritic schist, by tbe by, in great part) is 

 represented as a " fobated" rock dipping to tbe S.S.E., whilst we 



* Mr. Sharpe's sections indeed prove this ; for the lines of cleavage in his fig. 1 

 traverse the lines of foliation, which latter are, according to our views, indications 

 of the layers of deposition. 



t Phil. Trans. 1852. plate 24. 



J Unless his "fan-shaped" foliation represents the synclinals. 



