40 



which hears that name, and forms the extreme western spur of the great sustaininff 

 harrier to which I have just referred. The Ludlow Rocks of the Silurian regions 

 of England and Wales must be simply viewed as a continuation of the argillaceous 

 masses which prevail in the underlying formation of Wenlock Limestone and Shales. 

 The central portion, however, in several places, particularly at Aymestry, consists 

 of a dark grey clayey limestcme. The uppermost division of the series, i.e., the 

 Upper T>udlow, is more sandy and calcareous than the other portions, yet retains in 

 parts much of the " Mudstone " matrix, and is m great measure an imperfect thin- 

 V)edded, grey coloured, earthy building stone. Occasionally the highest stratum 

 is composed of light-coloured sandy freestones, through which the formation 

 graduates lithologically and comformably into the lowest beds of the Old Red 

 Sandstone, but the commingling of the two great series must have occupied a 

 very long jieriod of time, as the Passage Beds at LedVmry, which are not all Silu- 

 rian, nor yet all Old Red, have a thickness of nearly four hundred feet; never- 

 theless, these Passage Beds partake more of the latter formation than of the 

 former, and the fossils chiefly belong to the system of the Old Red, though pro- 

 bably evolved from the Ludlow Bone bed, which will be mentioned below. The 

 Lower Ludlow Rocks are an upward prolongation of the Wenlock series, and are 

 conxposed of dark -grey shale, rarel)' micaceous, with occasionally narrow bands, 

 an inch or two in thickness, and small concretions of impure limestone. They 

 attain at Ledburj' a thickness of seven hundred feet and upwards, and they sur- 

 round the valley of Woolhope within the wall of Aymestry limestf)ne. They 

 occur also in extensive tracts in Shropshire, Montgomeryshire, and in the valley 

 of the LTsk and other places. Throughout the typical districts these shales occupy 

 the base of the ridges, the harder summits and oiitward slopes of which are com- 

 posed of Aymestry limestone and Upper Ludlow rocks. The inferior strata, for 

 the most part argillaceous, are often arranged in large spheroidal masses, showing 

 a tendency to concretionary structure, which rapidly exfoliate under the atmo- 

 sphere and break into shivery fragments, as may be seen at any place and every 

 place where the stone lies for a few months, or sometimes for weeks only,' ex- 

 Iiosed. Calcareous nodules, difTering chiefly from those of the Wenlock deposit 

 in being usually of a darker colour, are often formed round an Orthoceras, or 

 a Trilobite, or other fossil as a nucleus. The occurrence of Graptolithus Priodon 

 (which is rare at Ledbury), Cardiola inteirupta, and Murchisonia Lloydii, prove 

 the indivisibility of the Silurian System of life. In ascending, the strata in some 

 places become somewhat more sandy, but it is not so at Ledbury ; at Woolhoj)e 

 and Leilbury and most other places it is the same dull non-micaceous shale, 

 which, from its want of cohesion, has been denuded for the most part, thus giv- 

 ing rise to deep valleys which separate the harder parts of the Wenlock and 

 Aymestry rocks from each other. This is very perceptible in the Woolhope 

 valley now before us, and at Ledbury, and is well shown in the great and highly 

 interesting Synclinal near Eastnor Castle. The Lower Ludlow stone is perfectly 

 useless for building, road making, or any other economical purpose, although, by 

 some extraordinary oversight it is being quarried, in common with Aymestry 

 limestone, but not to the same extent, and used for ballast on the new railway 



