THE SCHISTOSE ISLES. 285 



beds put on the appearance of a series of secondary 

 strata. The deception is often very great, and is much 

 aided by the thinness of the several beds which enter 

 into the chlorite series ; more especially by that of the 

 quartz rock and micaceous schist. This contrast of charac- 

 ter is one of the most remarkable features in the present 

 series as distinguished from that of micaceous schist ; the 

 latter rock, in almost every instance where it occurs 

 in Scotland, being confused, bent, undulated, and with 

 difficulty distinguishable into strata ; while the former, 

 even in its vicinity, maintains an invariable regularity 

 in every point throughout its whole extent. The re* 

 semblance to the secondary strata above mentioned, 

 is also much assisted by the perpetual interchange and 

 repetition of the different substances belonging to this 

 series ; each individual of it being succeeded by some 

 other of the number, and no stratum occupying more 

 than a few feet, while many of them do not exceed 

 two or three inches in thickness. 



' The extreme breadth of this collection of strata, taken 

 at right angles to the bearing, is twenty miles ; and as 

 the far greater portion of the beds occupy angles ap- 

 proaching the vertical line, from which the inclinations 

 on both sides tend in opposite directions, it may be 

 considered as the present thickness of the whole mass. 

 Having examined the sections in every point, from one 

 extreme boundary to the other, it may safely be stated, 

 that, from a mean measurement of the dimensions of 

 the separate beds, there are not less than 40,000 alter- 

 nations within the space of this series. It will be a 

 subject for future inquiry whether, admitting that all 

 such strata have been originally deposited in a horizontal 

 position, this can be considered as the actual and original 

 depth of the whole deposit. 



The general direction of the beds which form the 

 whole series, is, as might be expected, to the north- 



