490 King 8^ Lewis — U. Silurian and Old Red. 



ascends into D. L. lata at Saltwells is within 17 feet of D^, and at 

 Sedg-ley in the lower parts of D. 



The Downton Castle Sandstones (E) at Forge Bridge, Downton, 

 that are included in Ee, are thinly-bedded micaceous yellow sand- 

 stones. There are no such sandstones at Saltwells. Are they 

 represented at Saltwells by the rusty-red marly sandstones at the 

 top of E*^? At Saltwells E"* contains finer and more marly materials 

 than E*^ and E^ at Downton. Whilst Platyschisma helicites is very 

 abundant at Downton Castle Bridge, we have to search carefully for 

 a smaller species. L. Letvisii, which at Ludlow is rare in J)'^, ascends 

 abundantly in its smaller forms at Saltwells up to E''. The Downton 

 Sandstones at Saltwells are thicker, especially E'' and E^. At both 

 localities the massive yellow sandstones occur and have at their base 

 the important Platyschisma shale. 



The Saltwells Beds of Temeside age contain a quartzitic sandstone, 

 and are more marly than those at Downton. Our Fig. 4 compares 

 in thickness and zones very favourably with Miss Elles' and 

 Miss Slater's figs. 6 and 7. But L. viinima, rare at Ludlow in F*^, is 

 common at Saltwells within a few inches of F''. It is significant that 

 the two bone-beds, F*" and F**, and the two grit bands above are much 

 more calcareous than any Mr. King could find in the Temeside Beds 

 of the Downton district. Mr. Lewis finds that the composition of both 

 F*" and '^ varies in the diiierent samples of the same layer. Their 

 average composition is approximately 36 per cent of sand and clay 

 and 64 per cent of calcium carbonate. 



The Igneous Bocks. 



Mr. Lewis lias examined the igneous rocks. They contain olivine 

 (fresh), augite, often highly decomposed into chloritic products, 

 felspar, intermediate between labradorite and andesine, and small 

 quantities of magnetite. The felspar is centrally kaolinized, and 

 the rock is traversed by calcite of secondary origin. The magnetite 

 crystals show their crystal outline, and the felspars in rectangular 

 sections are embedded in plates of augite. The rock is entirely free 

 of glassy material, the residual magma having given rise to a second 

 generation of felspars and augite. The rock is therefore an ophitic 

 olivine dolerite. 



In tlie field all the forms of basaltic jointing are shown, the most 

 prominent being the spheroidal, with spheroids ranging up to a foot 

 in diameter. The line of junction between the aqueous and the 

 igneous rocks is distinctly marked. Fossils can be found at the 

 junction, so contact metamorphism is very limited. 



The dolerite is confined to the core of the anticline, and on both 

 sides of the axis of the fold it tapers off in sills, some of which run 

 into the Coal-measures. The dolerite appears as the crown of a 

 laccolite sending out tongues into the sedimentary series. 



There is an intimate relation between the faulting and the 

 intrusions. At Brewins Tunnel the dolerite can be seen following 

 the fault plane, and the microscope reveals incorporated fragments of 

 sand grains which form part of the fault rock. The intrusion is 

 therefore later than the formation of the W.S.W. to E.N.E. faults. 



