bearing on theoretical Speculations. 403 



the strata of the vicinity appear to have been subjected to the 

 violent action of disturbing forces. Lastly, In the actual geo- 

 logical period, including the whole time which has elapsed 

 since the continents assumed their present general form, the 

 violent action of the disturbing forces has been confined to 

 the districts of active volcanic vents ; districts, however, ex- 

 tensive if abstractedly considered, yet bearing no conceivable 

 proportion to the universal prevalence of these forces in the 

 earliest formations : in the same manner as the utmost con- 

 vulsions actually produced, though often considerable if 

 viewed in this isolated manner, yet sink into perfect insignifi- 

 cance if compared with the ancient disturbances effected in 

 our strata. 



Observations. — I would now examine rather more in detail 

 the principles thus generally enounced ; in doing which, I shall 

 be enabled to point out both what may be considered as al- 

 ready ascertained on the only sure foundation of patient ob- 

 serviition, and to indicate how much further those observations 

 must be extended, and in what directions they must be pro- 

 secuted, before we are in possession of sufficient data for any 

 thing like a complete Theory on all the points considered in 

 this article. 



First, then, I would state the general principle of the in- 

 vestigation. Suppose any number of stratified masses a, b, c, d 

 superimposed upon each other in the above order {a being 

 the lowest), and disturbed by dislocating forces. Suppose 

 them all to indicate the effects of these forces. 



It is evident that this may result from two different modes 

 of operation of those forces: for either, 1st, they may have 

 acted frequently during the formation of each of the affected 

 strata; or, 2ndly, they may have acted once only in a single 

 general convulsion subsequently to the formation of all the 

 strata. Now it is obvious, that in order to authorize any spe- 

 culation as to the prevalence of the disturbing forces at parti- 

 cular geological periods, we must first endeavour to ascertain 

 which of these cases has taken place. The only method by 

 which we can accomplish this, is to ascertain whether the strata 

 be conformable or unconformable ; for it is clear that the strata 

 which are conformable can alone be supposed to have been 

 affected by a single convulsion : for instance, a shock affecting 

 «, b, c, d at the same time would probably incline them all in 

 the same direction ; but, on the contrary, if a shock affected or, 

 before the formation of b, &c, it is clear that the latter could 

 not conform to the dislocations produced by that shock. 



To ascertain the conformity or non-conformity of the strata 



3 F 2 is, 



