Mr HOPKINS, ON RESEARCHES IN PHYSICAL GEOLOGY. 3 



sometimes in a regular vertical layer, and sometimes in irregular and 

 detached masses. I shall therefore occasionally, without wishing to pre- 

 judge the question of the formation of veins, speak of the fissures in 

 which they are deposited. 



a. The direction of the intersection of a vein with a horizontal plane 

 usually approximates to rectilinearity. It is not meant that every short 

 portion of this intersection forms a straight line, but, when considered with 

 reference to its whole extent, these variations are not for the most part 

 considerable. 



/3. In every mining district the largest and most important veins 

 are divided into two distinct groups, in each of which a very decided 

 approximation to parallelism is observable, and of which the directions 

 ai'e nearly perpendicular to each other. 



7. When the veins occur in stratified masses, the direction of one 

 of these systems usually coincides Avith that of the general dip of the 

 strata, the other being consequently perpendicular to that direction*. 



I. A large proportion of the most productive mineral veins are found 

 in the former of these systems. The latter (frequently termed by the 

 miner cross courses) carry ore very irregularly. 



e. It seems doubtful whether any actual limits of a fissure containing 

 a mineral vein were ever arrived at by the miner, though the division 

 of a large fissure into several small ones not unfrequently seems to 

 indicate a near approach to such a limit in the direction of its length. 

 I know of no case, however, in which such indications have been ob- 

 served of an approach to both extremities of a large vein. It is probable 

 that their linear extent is frequently much greater than has yet been, 

 or in many cases ever can be, observed. In numberless instances they 



* I first observed this relation between the general direction of the mineral veins and 

 that of the dip of the strata in the mining district of Derbyshire. I find on enquiry that the 

 same relation holds in the Alston-moor district, and in Flintshire. In Cornwall also, when the 

 lodes are in stratified rock, I apprehend this is generally the case, assuming the killas 

 formation in the immediate vicinity of the granite to be stratified. 



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