28 
SILUEIA. 
[Chap. IL 
< having not yet afforded signs of any former beings.' That few animals 
existed during the formation of these rocks has received support from the 
experiments of Dr. Daubeny, who has been unable to detect any phos- 
phate of lime in them, though in all the overlying Silurian formations in 
which animal remains occur there are abundant indications of that mineral. 
Even in the slender calcareous laminae discovered by Mr. Salter at Church 
Stretton, Dr. Percy could not detect any appreciable amount of the phos- 
phate. The determinations of the chemist are thus in perfect harmony 
with the conclusions of the geologist and palaeontologist, in establishing a 
decrement of life as we descend through the strata forming the crust of 
the globe. (See Appendix B.) Mr. Salter was so fortunate, however, 
as to discover traces of animal life in these old sediments. In several 
courses of the hard, siliceous, purple and grey flagstones, low in the series, 
and overlain by many thousands of feet of strata in which no fossils have 
been detected, he discovered certain indications of the existence of animals 
during the Cambrian period. 
The impressions represented in Foss. 2, f. 1, are described as the surface- 
holes made by Annelides, which, like the Lob-worm of our coasts, formed 
burrows in the sand. These impressions are distinguished by the name 
of Arenicolites didyma *. Together with the sinuous tracts or trails of 
such animals, Mr. Salter also found in the minute markings upon the rip- 
Fossil (2). 
Fig. 1. Fig. 2. 
Fig. 1. Burrows of Annelides allied to Fig. 2. Part of a Trilobite: Palseo- 
Arenicola. (Arenicolites didyma, Salter.) pyge Ramsayi, Salter. 
pled surface of the strata, evidence of littoral or shore conditions, — an 
inference which is strengthened by the occurrence of the beds of water- 
worn pebbles which are seen to prevail in the same series of strata as you 
ascend towards the summit of the Longmynd. 
The fossil next represented (Foss. 2, f. 2) is described by Mr. Salter as 
the caudal part, or pygidium, of a Trilobite, which he named Pakeopyge 
llamsayi. He considers it to be probably allied to the crustacean Dike- 
locephalus, described by Dale Owen, from some of the lowest beds of the 
' Silurian series ' of that author, in the region of Wisconsin, Iowa, and Min- 
nesota (United States) f. 
* Joum. Geol. Soc. Lond. vol. xii. p. 248. vol. xiii. p. 199. A head of the same kind of crus- 
t See the work, by Dale Owen, entitled ' Report tacean haa been since found by Mr. Marston, of 
of a Geological Survey of Wisconsin, Iowa, and Ludlow, in the same Longmynd beds, near Minton, 
Minnesota. Philadelphia, 1852. The Longmynd and is figured in the Chart of Fossil and Recent 
fossils are described in the Quarterly Journal of Crustacea, by Messrs. Salter, Woodward, and 
the Geological Society, vol. xii. p. 246, 1856; and Lowry, 1865. 
