36 Featherstonhavgh s Geological Report. 



vvacke 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 word 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, 

 with 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 the 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, with some new 

 species of avicula, pileopsis, some small orthocera and ichthy- 

 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 superior portion is an inorganic quartzose conglomerate, 

 overlying thick-bedded sandstone. 



