Between the Devonian and Silurian. 409 



is needed before the exact order and position of their different beds 

 can be considered as finally decided. 



I include in these " transition beds " all from the top of the Upper 

 Ludlow to some thin flaggy micaceous sandstones, which I consider 

 the base of the Old Eed. The junction of these beds with the Old 

 Eed Sandstone may be observed in the section on the Shrewsbury 

 and Hereford Eailway, near the Ludlow Tunnel, and also at the Tin 

 Mills near Downton, The lowest of these transition beds is the 

 Downton Sandstone, the commencement of which I would fix at the 

 PlatyscMsma bed, which is a well defined line, and where it partakes 

 in some measure of the Upper Ludlow character' of rock. The prin- 

 cipal fossils found in it are Lycopodiaceous seeds, Pteraspis Banhii, 

 P. truncatus, Eurypterus linearis, Pterygotus gigas, P. JBanksii, Leper- 

 ditia marginata, Beyrichia Kloedeni, Annelids, Carbonaceous remains, a 

 species of Modiolopsis, and Lingula cornea. Of these fossils, Leper- 

 ditia marginata has not been found in the Upper Ludlow, and Euryp- 

 terus, Pterygotus, and Pteraspis are much more abundant in the 

 Downton Sandstone than in the underlying rock ; all of which fossils 

 reach their greatest development in the thin band occurring about 

 300 feet higher up, called the Olive or Tin Mill Shale. Eurtjpterus 

 linearis has been found in the Upper Ludlow, a few feet below the 

 Downton Sandstone, and just above occurs the Bone Bed, a stratum 

 from 1 to 6 inches thick, composed of fragments of fish and crusta- 

 cean remains. 



The Downton Sandstone is composed of fine yellow-coloured sand- 

 stone, deposited in a tranquil sea, the currents of which for long 

 periods carried the same materials ; it had, therefore, everything 

 favourable for the preservation of its organic life. Between this 

 rock and the next to be described occurs a series of different coloured 

 bands of sandstone, showing great irregularity in their formation, 

 which is not favourable to the preservation of their fossil contents, 

 and consequently in these beds we find a scarcity of organic remains • 

 I only know of one organism obtained from them, the small Beyrichia. 

 The next bed is a greenish-grey sandstone, strongly micaceous ; the 

 only fossils that have yet been found in it being Cephalaspis Murchi- 

 soni, Lingula cornea, and a few Carbonaceous remains. This bed may 

 be observed in position in the lane leading from Onibury to Norton, 

 and at the Tin Mills near Downton. 



We next come to the Olive shales, which are thin light-brown argil- 

 laceous beds, very brittle and full of fossils, and these latter generally 

 occurring in thick masses. About the centre of these beds is the 

 Upper Bone Bed, from whence very fine spines of Onchus Murchisoniy 

 Onehus tenuistriatus have been procured, also fragmentary remains of 

 Cephalaspis Murchisoni, C. ornatus, Auchenaspis Salteri, etc. From 

 the Olive or Tin Mill Shale has been procured Pterygotus Banksii, 

 Eurypterus pygmceus, E. megalops, and E. acuminatus ; Leper ditia mar- 

 ginata, Beyrichia sp. remains of plants, a species of Actinophyllum, a 

 new Modiolopsis and Lingula cornea. The best sections at present 

 known may be seen on the Shrewsbury and Hereford Eailway, at 

 the Tin Mills, and near Onibury. 



