544 ,ISLE OF MAN. GEOLOGY. SCHIST. 



where the band of graywacke appears, although, in Isla, 

 it extends through both ; but there is no difficulty in 

 explaining this circumstance, when it is recollected that 

 many of the graywackes occurring with clay slate, are 

 of a solid and non-fissile structure. The band in question 

 may therefore be considered as the edge of a bed of 

 this rock, deposited in alternating order with the clay 

 slate. This bed, on the foregoing principles, will therefore 

 serve to determine the position of the great strata of 

 schist, of which the seams are here invisible ; and they 

 will thus be found to lie nearly at right angles to the 

 direction of the fissile tendency. Instead therefore of 

 considering the schist in the neighbourhood of Douglas 

 as placed in an erect position, it must be considered 

 as disposed in horizontal beds ; and, if the same rule 

 could be proved to hold good every where in this island, 

 we must in every instance reverse the most obvious 

 appearances ; considering the beds to be erect where 

 the fissile tendency is horizontal, and horizontal where 

 this is erect. Such an universal conclusion however 

 would not be justified ; but these considerations inculcate 

 the necessity of caution in assigning the positions of 

 the beds of schist, unless, either the indications just 

 mentioned are visible, or the positive existence of the 

 seams is ascertained. 



The seams themselves are visible near Spanish head, 

 and they are horizontal or nearly so ; while they are at 

 the same time slightly undulated : but there is here 

 no ready access to them, so as to determine at what 

 angle the fissile tendency lies. In most other parts of 

 the island, extreme confusion in the fissility is visible, 

 but the seams of the beds are scarcely ever to be dis- 

 covered. If we cannot safely conclude from this cir- 

 cumstance, that the beds themselves are disposed in 

 an undulating and irregular manner, that point must 

 remain unsettled, since there are no other indications 

 from which to form a judgment. 



