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has been completed before any great amount of pressure was 

 applied ; and thus the forms were preserved in relief In the 

 process of fossilization, the horny substance of which they were 

 formed has been replaced either by some form of Carbon, or by 

 Iron Pyrites. The latter is the form in which Skiddaw Slate 

 fossils are almost invariably found. 



There is reason to believe that only a very small percentage of 

 the Graptolites were fossilized ; the remainder would decay and 

 become mixed with the mud at the bottom of the sea, and thus 

 supply the carbon that forms one of the constituents of the rocks 

 in which they are found. Some of the slates and shales that yield 

 Graptolites most plentifully, contain as much as five per cent, of 

 carbon, perhaps derived from the decayed remains of these little 

 creatures : indeed, some geologists have suggested that the dark 

 colour and the anthracitic appearance of the most highly-fossiliferous 

 beds may be due entirely to that cause. 



There is yet need for active and zealous workers to assist in 

 solving one of the most difficult problems connected with the 

 geology of the Lake District, namely, to determine the true position 

 of the Skiddaw Slates. The late Mr. Ward, who laboured with so 

 much enthusiasm in mapping the rocks of this district, cautiously 

 refrained from a definite expression of opinion in his memoir of 

 the " Geology of the Northern part of the Lake District," but 

 quotes the opinions of Mr. Salter and Professor Nicholson, whose 

 palaeontological researches led them to agree in placing the Skiddaw 

 Slates on the same horizon as the Lower Llandeilo Rocks. But 

 in Mr. Ward's "Physical History of the Lake District," published 

 a few years later, he states distinctly that, from physical and 

 palaeontological evidence combined, he considers the Skiddaw 

 Slates to be in part the equivalent to the Welsh Arenig Rocks; also 

 that the Arenig Grits, Tremadoc Slates, and Lingula Flags are all 

 represented in the lower part of the Skiddaw Slate Series. Some 

 geologists, however, dissent from Mr. Ward in regard to the last 

 named stratum, while others disagree with him in reference to the 

 relative positions occupied by the Skiddaw Slates and the Volcanic 

 Series of Borrowdale, contending that the latter is an older, and 



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