36 



Featherstonhaugh^s Geological Report. 



wacke also. The same objections which apply to the term 

 transition, apply to the term grauwacke. The different form- 

 ations of the Silurian and Cambrian systems are distin- 

 guished by fossil remains peculiar to each of them, and noth- 

 ing would more retard the progress of scientific perspicuity, 

 than to retain an inharmonious term which is hardly definable, 

 merely because certain rocks having an affinity in mineral 

 structure are found repeated in various parts of them. The 

 term grauwacke seems originally to have been used by 

 the miners as a provincial w^ord to express the character of 

 those conglomeritic beds formed of gravelly fragments of 

 various sizes of the older rocks, imbedded in a paste of slaty 

 matter, which are even occasionally found in the coal meas- 

 ures, and which abound sufficiently in the formations sub- 

 jacent to the carboniferous limestone, to justify the belief that 

 an immense period of time must have elapsed between the 

 first appearance of these conglomeritic beds and the deposite 

 of the carboniferous limestone. We can no longer, however, 

 wath any propriety, retain this term for the beds immediately 

 subjacent to the old red sandstone, since Mr. Murchison shows 

 that his Silurian system, in which those beds are compre- 

 hended, contain few if any of those beds which were first 

 named grauwacke by the German mineralogists. This term, 

 if at all continued, will probably be restricted hereafter to 

 some of the beds of tlie Cambrian system. 



Old red sandstone. Mr. Murchison proposes to divide this 

 formation into three parts : the lowest consists of flaggy, high- 

 ly-micaceous, hard, red and green sandstone, v/ith some new 

 species of avicula, pileopsis, some small orthocera and ichthj^- 

 odorulites. The central portion is formed of red and green 

 < concretionary limestones, with spotted argillaceous marls and 

 beds of sandstone, containing undescribed genera of Crustacea. 

 The supeiior portion is an inorganic quartzose conglojnerate, 

 overlying thick-bedded sandstone. 



