252 MINERAL SPRINGS — AGRICULTURAL CHARACTERS OF THE SILURIAN ROCKS. 



up of dislocated strata, the depth of the wells necessarily varies much within very short distances. 

 Thus at Clungunford, the wells being from four to seven yards deep, are pretty constant, while 

 at Wigmore, in shale of the same age, one source twenty-three yards deep occasionally fails, another 

 twenty-six yards being constant. 



Mineral Springs. 



The absence of all simple minerals except a very little iron pyrites in the Upper Silurian rocks near 

 Ludlow, renders it improbable that they should contain mineral springs. One, however, is known, 

 the nature of which may be implied from its name the " Saltmoor spring." According to a rough 

 analysis of Dr. Lloyd it contains the sulphates of soda and lime, with oxide of iron and sulphuretted 

 Irydrogen gas, but the supply of some of these ingredients is very uncertain 1 . 



Although the bed from which this spring rises is not exposed, there can be no doubt that it is the 

 upper stratum of the Ludlow rock, since that rock is visible at the surface very near this spot, and 

 the well is directly in the prolongation of the edge of the outlier of Tinker's Hill, Caynham Camp, 

 and just where the Ludlow rock subsides beneath the Old Red Sandstone. It has been previously 

 shown that these upper strata occasionally contain sulphuret of iron, from the decomposition of 

 which the contents of the well may in great part be derived ; but I would further remark that the 

 spring, like others before-mentioned, is situated upon one of the lines of dislocation parallel to the 

 axis of the Ludlow promontory. This fissure, indeed, is a direct prolongation of the great basaltic 

 dyke which penetrates the adjacent coal measures of the Clee Hills. (See Map and p. 126.) In 

 chapters 26 and 27 I shall show that other mineral springs in Radnorshire and Brecknockshire in- 

 variably issue from such points of dislocation, particularly where rocks of volcanic origin have burst 

 through, fractured, and altered the sedimentary deposits. The same may be said of the Admaston 

 Spa near the north-western edge of the Wrekin. 



Agricultural Characters of the Silurian Rocks. 



Viewed as a whole, the Ludlow and Wenlock formations or " Upper Silurian " rocks 

 are so argillaceous, that where not covered by transported materials, their decomposition 

 gives to the surface a distinctive character. Thus no one can fail of being much struck 

 in passing from the Old Red to the Silurian System at the change in the colour, and the 

 diminished richness of the soil belonging to the latter. This observation, however, 

 requires explanation. The Upper Ludlow rock, for example, when composed of an ad- 

 mixture of sand, clay, and lime, may even he termed a good agricultural substratum ; 

 witness the produce on the slopes of the rock forming the external faces of the Ludlow 

 promontory, where noble trees 3 are rivalled by excellent crops of barley, oats, and turnips. 



1 I should apologise to Dr. Lloyd for quoting his rough analysis. He observes that this Saltmoor water 

 closely resembles that of Harrowgate in medicinal properties. 



2 The woods of Downton Castle may be specially cited, and the Spanish chestnut trees of Croft Castle are of 

 remarkable size. On the whole, however, the oak timber grown upon the Ludlow rocks is of less value than 

 that of the Old Red Sandstone. As specimens of the latter, see the venerable trees of Oakley Park and the 

 gigantic oak of Nun Nupton near Brimfield. 



