41 



now being constructed there, for which purpose it is utterly unfit, consequently 

 opportunities for examining its structure and obtaining its fossils do not very 

 frequently occur. The heavy railway works now in progress at Ledbury afford 

 extraordinary advantages for obtaining additional knowledge relating to it, of 

 which every advantage should be taken by geologists. The Aymestry Limestone 

 is a subcrystalline earthy rock, arranged in beds from one to five feet thick, the 

 laminae of deposit being marked by layers of shells and corals. The rock when 

 unweathered is of indigo, or bluish-grey colour, in parts mottled by the mixture 

 of white calcareous spar. It is regarded by some as only a calcareous condition 

 of the Lower Ludlow formation. The quarries, like those in all the harder bands 

 of the Ludlow formation, present natural backs or divisions, usually coated by a 

 dirty yellow or greenish shale of an ochreoiis character. These are the faces of 

 joints more or less vertical, and when open, they occasion the rock to separate 

 into rhomboidal masses, which are easily detached if the strata are much inclined. 

 The rock is, therefore, subject to slides and subsidences, particularly where the 

 underlying saponaceous "Walker's Clay," or Fuller's earth prevails, bands of 

 which are frequently found near Ledbury varying in thickness from a mere 

 marking to a depth of one or two inches. Great risk is ran in building on slop- 

 ing ground of this character. Examples of these slides may be seen on many 

 spots, particularly at the "The Wonder" at Marcle, and at Dormington and 

 Backbury, and also on a smaller scale in many instances round the outside of the 

 Valley of Woolhope. In the Woolhope Valley the Aymestry rock assumes pre- 

 cisely the same external or physical features as at Ledbury and Ludlow, having 

 from its hardness resisted denudation better than other portions of the deposit. 

 It thus forms the crest of the external and encircling ridge, and is prominent in 

 the hills of Seager and Backbury and the Cockshoot, and is quarried for road and 

 other purposes all along the flanks of these eminences. There are whole hills of 

 it at Ledbury and Eastnor, but the finest open section is at Rock Hall quarry, 

 near the village of Aymestry, whence it takes it name, and where the huge 

 Pentamerus Knightii is found. It is seen also in Staffordshire and Shropshire, 

 at Usk, May Hill, Abberley, Eastnor, and Coddington, and the interesting out- 

 lier Shucknall Hill is of this formation. The Li^pper Ludlow Rock is the most 

 diversified in stnicture and contents of the three sub-divisions of the highest Silu- 

 rian formation, and is also remarkable in exhibiting a transition into the next 

 overlying system, the Old Red. Its lowest stratum is a calcareous shelly band, 

 charged with Rhynconella navicula, and occasionally attains a thickness of 30 or 

 40 feet. This is surmounted by the gi'ey calcareo-argillaceous masses, so common 

 throughout the Silurian rocks, which, from their incoherent nature, easily 

 decompose into mud. The chief and distinguishing portion of the Upper Ludlow 

 contains more calcareous matter and sand than the beds immediately beneath. 

 It is, on the whole, a slightly micaceous, thin-bedded stone, of bluish-grey colour 

 within the solid portions, but weathering externally to a brown rusty grey, and 

 remarkable for its symmetrical transverse joints. It is used extensively for build- 

 ing, but if not placed horizontally in the wall is prone to decomposition. It is 

 largely developed round the outsides of the Woolhope valley, and at Ledbury, 



