Caution in regard to Shifts. 51 



cut through the strata in unbroken and continuous lines."* 

 If we were not more concerned here with the use of these phe- 

 nomena in the discovery of valuable minerals than with their 

 explanation, we should express the opinion that that explana- 

 tion which comprehends all these facts, and hence is the most 

 generally applicable, is also the most natural and most accep- 

 table. 



Caution in regard to Shifts. — Another phenomenon would 

 seem to have been confounded with what we have been describ- 

 ing. It has been found that different rocky masses, often of 

 very considerable size, meet together in the direction of their 

 strike, without our having an opportunity of ascertaining the 

 exact boundary, and the conclusion has thence been also de- 

 duced, that there exists a shift of immense extent. An ac- 

 quaintance with the boundary or junction would have taught 

 the observer that there is no shift, but, on the contrary, that 

 the usual relations of superposition, accompanied by transi- 

 tions, or other previously mentioned appearances, present them- 

 selves. 



As the secondary rocks include districts which are bounded 

 by two, or perhaps by several mountainous tracts, and as their 

 relations of superposition, especially when they are not modi- 

 fied by particular relations of structure, or the latter taken for 

 the former, depend upon their fundamental rock, it hence fol- 

 lows, that, towards the base of the mountains, they possess a 

 more inclined place or position, and their outgoings appear 

 more frequently at the surface than in the interior of the space 

 they occupy, where their position approaches more nearly the 

 horizontal, and where sections are only to be expected in con- 



» " As the whin-dyke, previously described, does not pass through the 

 Beaumont coal-seam, Mr Buddie, from whom the particulars are derived, 

 considers that this and other facts show it to be an exception to the gene- 

 rally received opinion, that whin-dykes have been formed by the basalt in a 

 state of fusion, having always been forced upwards through the fissures into 

 the stratification from below, and that they extend to an indefinite depth. 

 It is also doubtful whether those basaltic fissures which occur in various 

 parts of the Newcastle coal-field run through the strata in uninterrupted 

 and continuous lines." Vide the history and description of Fossil Fuel, 

 p. 1C5. Passage from the Transactions of the Natural History Society of 

 Newcastle. 18*^0. 



