THE SCHISTOSE ISLES. 289 



beds, not however placed in the middle of the tract; 

 towards which the strata converge on each side, both from 

 the south-eastern and north-western boundaries. 



It is now necessary to enter on the description of the 

 several rocks which enter into this series; a task the 

 more necessary, as these details were purposely omitted 

 in treating of the Chlorite isles. The peculiar nature 

 of these substances, no less than the peculiarities of 

 general character just described, were the circumstances 

 which induced me to consider the Chlorite series of this 

 coast as distinct from that of the micaceous schist. It 

 remains to be known whether any series analogous to 

 this exists in other countries; but that can never be 

 determined if every schistose rock of this character is con- 

 ceived to belong to the series of micaceous schist, since 

 investigation then becomes unnecessary. It remains for 

 geologists to reject it, if they please, as a superfluous 

 distinction; but, in the present state of this science, 

 it is preferable to "err on the side of extreme refinement, 

 than to confound under general terms, details, the ulti- 

 mate value of which must yet be unforeseen. That every 

 member of this series does or may occur, either with 

 the series of micaceous schist or that of gneiss, is no 

 argument against the present division, since the same 

 is true of many other rocks. The establishment of 

 certain distinct series, in which a peculiar general order 

 and association of a given number of substances is 

 observed, is not one of the least improvements in modern 

 geology. The importance of the formations of geologists 

 is too well known to require defence. 



In describing the several strata which enter into the 

 Chlorite series, (or formation,) it appears expedient to 

 divide them into two portions, those which are of most 

 frequent recurrence and of the most constant character, 

 and those which present various modifications, both 

 subordinate in quantity and apparently variable in com- 

 position. The leading strata which give the character 



VOL. ii. u 



