140 LUING. GTIOLOGY. 



between the bed and the laminar disposition; but as 

 this subject will be examined more fully hereafter when 

 more difficult cases occur, I shall not now dwell on 

 the distinction, but simply state it as the test here used 

 in distinguishing the fissility from the stratification. 

 Although both of these are thus generally conformable in 

 this place, the lamination, in some cases, lies obliquely 

 to the stratum; that obliquity being however but small; 

 whereas in Isla, as I shall hereafter show, it forms a 

 very considerable angle with the plane of the bed. This 

 circumstance, like the former, is attended with some 

 obscurity ; since, in some cases, the lamination of the 

 slate would appear to be the mere result of its mode 

 of deposition, while in others it must necessarily have 

 arisen from a concretionary arrangement. It is doubtless 

 more simple to consider the fissile direction as in all 

 cases the consequence of the latter cause, than to assume 

 both as having acted on different occasions ; but it by 

 no means follows that the simplest solution is the true 

 one ; since, in the more recent schistose substances that 

 contain organic remains, the position of those would 

 often seem to indicate that this tendency is the con- 

 sequence of the mechanical arrangement. In a few places, 

 the laminae of the clay slate, as well in this island as 

 in Torsa, are found to be contorted ; and, generally, in 

 planes with a single curvature, the axis of which is 

 parallel to the plane of the bed. As it did not appear 

 that in these cases the beds themselves were bent, but 

 that the flexure was limited to the laminae, it is probable 

 that this disposition is also a result of some modification 

 of the concretionary structure. But it is a fact of too 

 much importance in the general history of the schistose 

 rocks, to be determined on evidence so imperfect and 

 so limited. The contortions so frequent and remarkable 

 in micaceous schist, will naturally occur to the reader's 

 mind as admitting of a similar explanation. But in all 

 those which 1 have examined in lliis latter rock, t 



