30 LOWER AND UPPER SILURIAN FORMATIONS : 



[It may be proper here to advert parenthetically and provi- 

 sionally to a larger sub-Silurian fauna, which has now (1860) 

 been established. Briefly, the beds of conglomerates, sand- 

 stones, and schists, constituting the Longmynd Hills, in Shrop- 

 shire, described by the Government surveyors as 26,000 feet 

 in thickness, arguing a vast space of time for their deposition, 

 exhibit on their slab-surfaces marks of the burrowings of 

 marine worms, and have also presented a fossil (Palceopyge 

 Ramsayi], believed to be crustacean, and most probably a 

 trilobite. While the grits of Harlech, in North Wales, and 

 some coarse sandstones near Bangor, present, like the Skiddaw 

 slates, remains of sea-weeds, an equally ancient grawacke at 

 Bray-head, in Ireland, has furnished remains of two species of 

 polype (Oldhamia antiqua), and the sub-Silurians of Suther- 

 landshire have afforded a branched zoophytic form, provi- 

 sionally referred to the Bryozoa. As far as a very limited 

 amount of positive evidence carries us, we have now a first 

 zone of life even more remarkably deficient in important 

 animals than that hitherto taking this position.] 



Taking the Lower Silurian formation as a whole, and in- 

 cluding any fossiliferous rocks that may be ascertained to be 

 lower, ikefatma or assemblage of animals which it contains 

 must be pronounced humble, though it is not deficient in & 

 class which stands high in the sub-kingdom to which it be- 

 longs. What constitutes high and low in animal organization ? 

 An animal is said by naturalists to be low, when its organiza- 

 tion is of a simple kind, subservient to a comparatively narrow 

 range of functions, and suited to a comparatively narrow field 

 of existence if, for instance, like the polypes, it be fixed in 

 situation, and consist mainly of an alimentary receptacle, with 

 means of filling that with food. Elevation is marked in the 

 scale by an animal ceasing to be compound (which is the case 

 of the coralline polypes), assuming a power of locomotion, 

 having sex assigned to separate individuals, exchanging a mul- 

 tiplicity of parts serving one end (as the many pairs of feet in 

 the centipede), for a smaller number ; attaining, in short, at 

 once a more complex and more concentrated organization. 1 

 On such ground the animal kingdom is primarily divided into 

 Vertebrate and Invertebrate ; animals with a back-bone, and the 

 superior nervous system which that structure implies ; and 



1 In the highly organized animal " the number of dissimilar parts is 

 larger, and the consequent adaptation of the whole to a variety of pur- 

 poses is more complete." Carpenter. 



