18 PHILOSOPHICAL TRANSACTIONS. [aNNO 1791. 



One consequence of these observations is too important to be omitted. They 

 lead us to reject the common division of mountains into primary and secondary. 

 The chains of granite, schistus, and limestone, must be all coeval ; for if the 

 central chain of the Alps burst as a body expanded by heat from the bowels of the 

 earth, it reared the bordering chains at the same effort. But it must be recol- 

 lected, that the mountains no longer wear their original form, valleys having been 

 cut between and through them, and various other effects of dilapidation having 

 taken place. It is by no means difficult to understand why no exuviae of or- 

 ganized bodies are found in these imaginary primitive mountains. Rising from a 

 great depth, they threw aside the superficial accumulations of the ancient ocean. 

 What was deepest is therefore now most central; and what lay on the surface 

 now skirts the high interior chains. Hence the strata rest indifferently on granite, 

 basaltes, or lava ; all which substances derive from their situation an equal claim 

 to be regarded as primordial materials. It is a little surprizing, that this inveterate 

 error, which has effectually barred the way to all great discoveries in geology till 

 of late, should have prevailed so long : for, 1. it is well known, that granite is 

 sometimes found inclosing pieces of schistus ; nor are long stretches of slate un- 

 common in mountains of granite. Now, how can a secondary be so enveloped in 

 a primitive rock ? and how easy is this to be understood, if we suppose granite as 

 a fused mass raising, rending, and shivering the incumbent strata, while its heat 

 hardened them into laminated stone. 2. Supposing granite mountains previously 

 existing in the ancient ocean, the inclination of the incumbent strata, and their 

 disarrangement is such, that they could never have been deposited as they appear 

 at present ; they would have been much more horizontal in their direction. It 

 seems impossible to attribute the disorderly deviation, which is so general in the 

 mountains of slate, &c. from that position which all sediments from water assume, 

 to any thing but a force lifting from below, and sometimes bursting through. It 

 is also certain, that all these lifting masses, from granite to acknowledged lava, 

 are found squeezed up through fissures formed in the strata by their own expan- 

 sion. This, and not the infiltration of water, as M. de Saussure would persuade 

 us, appears to be the true origin of such veins of granite. 



IV. On Nebulous Stars, properly so called. By M^m. Herschel, LL. D., F.R.S. 



p. 7J. 

 In one of his late examinations of a space in the heavens, which he had not re- 

 viewed before, Dr. H. discovered a star of about the 8th magnitude, surrounded 

 with a faintly luminous atmosphere, of a considerable extent. The phenomenon 

 was so striking that he could not help reflecting on the circumstances that at- 

 tended it, which appeared to be of a very instructive nature, and such as might 

 lead to inferences which will throw a considerable light on some points relating to 

 the construction of tlie heavens. 



