134 ON THE CHARACTERS AND DISPOSITION 



rock exists in a continuous state beneath, and that its 

 apparent insulation is the result of the absence of the 

 superincumbent strata at those particular points. In 

 the case of trap, on the contrary, where there are not 

 reasons for supposing that the deposits have been 

 partial, it is often easy to discover that their insulation 

 arises from their own waste ; the thinner or feebler 

 connecting portions having been destroyed while the 

 others have remained. 



It is easily inferred from the above remarks, that, 

 of the unstratified rocks, one set is inferior to all the 

 strata, and another superior to them. But with re- 

 spect to trap, at least, this is not exclusively true: 

 whether it be the case with granite, is a question that 

 will be better discussed in another place. The rocks 

 of that division are found beneath the strata, as well 

 as above them, in masses so large and so irregular 

 that they cannot be ranked among veins, otherwise 

 than as every finite mass included among stratified 

 rocks may claim to be considered as such. If a mass 

 of trap, indefinite downwards, should be found be- 

 neath the strata, then, by the postulate on which the 

 distinction adopted in this work is founded, it becomes 

 granite. That question being connected with the 

 one which relates to the possible superincumbent po- 

 sition of granite, will be considered in a more proper 

 place. (Chap, xxtv.) 



The forms of all the unstratified rocks are irregular, 

 and, in the majority of instances, totally dissimilar 

 from those of strata. It is owing to this absence of 

 the stratified form and disposition, that we are unable 

 to infer the continuity of the rocks under review, 

 when that is not actually visible. It may be supposed, 

 it is true, that if granite exists beneath all the strata, 

 so as to form their immediate foundation., every mass 



