232 ON THE ORIGIN, MATERIALS,, COMPOSITION, 



Of Transitions among Rocks. 



The last question respecting rocks that appears to 

 require examination, relates to the transitions, real 

 or imaginary, that take place between different kinds. 

 Being formed, as we have seen, of so few substances, 

 and possessing so many analogies among each other, 

 such transitions ought to be expected. That they 

 exist, is no reason for an hypothesis which has been 

 maintained on this subject. 



Because there is a gradation of a certain kind 

 among gneiss, micaceous schist, and quartz rock, and 

 because it is possible, by selecting particular speci- 

 mens, to make that transition still more extensive, it 

 has been argued that all these rocks originated at one 

 time, from a common solution, and were therefore 

 the results of a continued crystallization from a fluid 

 gradually varying. They who have chosen to main- 

 tain this doctrine, have certainly derived from it 

 great convenience ; inasmuch as they have dispensed 

 with the labour of investigating the differences of 

 these rocks, or describing their characters and con- 

 nexions. I know not what advantages are to be 

 gained by thus restoring Geology to its original 

 chaos ; and as the question of watery crystallization 

 has been sufficiently considered in other parts of this 

 work, that subject may be dismissed. 



Such transitions as do actually occur, may easily 

 be accounted for in various ways. In the older 

 strata, they may arise from proximity of position, in 

 rocks that have been in a state of semifusion and that 

 were formed of similar materials. Thus they are com- 

 mon between gneiss, micaceous schist, and quartz 

 rock, accordingly as these approximate. Thus, by 



