ISLE OF MAN. GEOLOGY. SCHIST. 541 



position in different places bears any relation to the granite 

 mass, or rather to the forms of the mountains; since the 

 quantity of granite here visible is too trifling to admit of 

 any comparison of this nature. To determine this point, it 

 would be necessary to assign the positions of the strata on 

 different sides of the mountain range; an object which 

 renders it first indispensable to ascertain to what extent 

 proofs of the stratification of the schist can here be obtained. 

 The indications of this order are seen in many instances 

 so distinctly, that no doubt can be entertained respecting 

 the stratified nature of argillaceous schist. But the dis- 

 position of the strata, as formerly observed, is sometimes 

 easily confounded with that of the laminar structure, which 

 is not always coincident, but is, on the contrary, some- 

 times placed at considerable angles with the plane of 

 stratification. This error is easily committed in examining 

 the schist of this island, but it may be corrected by careful 

 examination. But that examination, although sufficient to 

 determine that the laminar tendency of the schist is here 

 often different from the plane of stratification, has not 

 enabled me to assign the real positions of the strata, if 

 indeed they can be discovered to such an extent as to 

 determine the object in question, namely, the relation of 

 the strata to the forms of the mountains. To understand 

 this part of the subject, however, it is necessary first to 

 describe the schist in some detail, and thus to state the 

 causes of this uncertainty. 



The substances which appear to be predominant in the 

 general mass, are those which mineralogists have agreed 

 to rank with clay slate ; - although many of them differ 

 materially in their composition and appearance, from the 

 best defined specimens of that rock. Together with these, 

 there occurs, but in comparatively small quantity, that 

 schist distinguished by the term graywacke ; generally of 

 a fine texture, and presenting a much more limited variety 

 of appearance than is usual in similar situations. It is found 



