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Ch. VII.] 



PARALLEL MOUNTAIN-CHAINS. 



129 



encounter, when we attempt to apply the theory nnder con- 

 sideration even to the best known European countries, is 

 afforded by what is called < The System of the Longmynds.' 

 This small chain, situated in Shropshire, is the third of the 

 typical systems to which M. E. de Beaumont compares other 

 mountain ranges corresponding in strike and structure. The 

 date assigned to its upheaval is 'after the unfossiliferous 

 greywacke, or Cambrian strata, and before the Silurian.' But 

 Sir E. I. Murchison had shown in 1838, in his * Silurian 

 System,' and the British Government surveyors, since that 

 time, in their sections (about 1845), that the Longnrynds and 

 other chains of similar composition in North Wales are post- 

 Silurian. In all of them fossiliferous beds of the lower 

 Silurian formation or Llandeilo flags are highly inclined, and 

 often vertical. In one limited region the Caradoc sandstone, 

 a member of the lower Silurian, rests unconformable on 

 the denuded edges of the inferior (or Llandeilo) member of 



group ; whilst in some cases both of these sets of 

 strata are upturned. When, therefore, so grave an error is 

 detected in regard to the age of a typical chain, we are 



same 



means 



parallel chains in France, Germany, and Sweden, assumed to 

 be ' ante- Silurian/ have been made to agree precisely in date 

 with the Longmynds ? If they are correctly represented as 

 having been all deposited before the deposition of the Silurian 

 strata, they cannot be contemporaneous with the Longmynds, 

 and they only prove how little reliance can be placed on 

 parallelism as a test of simultaneousness of upheaval. But 

 in truth it is impossible, for reasons already given, to demon- 

 strate that each of those nine chains coincide in date with 

 one another, any more than with the Longmynds. 



The reader will see in the sequel (Chap. XXXII.*) that 

 Mr. Hopkins has inferred from astronomical calculations, that 

 the solid crust of the earth cannot be less than 800 or 1000 

 miles thick, and may be more. 



depth of a hundred miles, such a thickness would be incon- 

 sistent with M. E. de Beaumont's hypothesis, who requires 



Even if it be solid to the 



mile 



or even less. Mr 



* For page, see Index, vol. ii., ' Hopkins. 



VOL. I. 



K 



