762 C. CALLAWAY ON THE QUAKTZITES OF SHROPSHIRE, 



determination till decisive evidence is forthcoming. The quartzite, 

 then, is older than the Ffestiniog period. But the Hollybush and 

 the quartzite do not succeed each other conformably. In the 

 Wrekin area the dips are so discordant as to suggest a considerable 

 gap. The quartzite, in most cases, dips away from volcanic bosses, 

 and the direction of dip is determined by these local upheavals. 

 But the dips of the Hollybush are subject to no such law. Their 

 general direction on the south-east of the Wrekin, where the 

 quartzite dips south-easterly, is to the south-west ; but in one place 

 they appear to conform to the dip of the quartzite, and at a little 

 distance they plunge at a high angle to the north-west (that is, 

 towards the quartzite). South of Charlton Hill, also, the sandstone 

 dips towards the quartzite. The apparent conformability of the 

 two formations at Caer Caradoc cannot counteract such clear evi- 

 dence of discordance. Parallelism of strike does not prove con- 

 formity, since a strike fault might let down the upper of the 

 formations without producing any alteration in the dip or strike. 



It is clear, therefore, that the quartzite is older than the Holly- 

 bush Sandstone by a gap, and, consequently, cannot belong to any 

 part of the Upper Cambrian series. 



Three hypotheses now remain. The quartzite may be on the 

 horizon of the top of the Lower Cambrian ; or it may belong to the 

 Lower Cambrian, or it may be Precambrian. 



a. The top of the Lower Cambrian {Longmynd series). — The Lower 

 Cambrian of Shropshire, as is well known, is a great series consisting of 

 fine-grained slates or hardened shales in the lower part, and of sand- 

 stones and conglomerates above. For reasons which I cannot here 

 detail, I believe that neither the base nor the top of the succession 

 is seen, being cut out by faults. Does the quartzite represent a lost 

 capping of the Longmynd rocks? I think the great discordance 

 between the quartz-rock and the Hollybush Sandstone decisively 

 negatives this supposition. 



b. The Longmynd Series. — No band of quartzite has been observed 

 in this series from top to bottom. If the quartz-rock represents any 

 part of the Longmynd succession, where are the beds which on this 

 supposition should intervene between the quartzite and the Precam- 

 brian volcanic series ? Or is the quartzite a basement of the Longmynd 

 rocks ? If so, there should surely be some concordance of dip and 

 strike. But the Longmynd strata in their lower part almost uni- 

 formly dip at very high angles to the west-north-west, whereas 

 the quartzite, as previously shown, dips away from volcanic bosses 

 at the most varied dips and strikes. 



c. Precambrian. — On the rejection of hypotheses a and 6, the 

 balance of probability is decidedly in favour of this supposition. 



4. The Fauna of the Quartzite. 



For years I searched for fossils in vain ; but since I commenced 

 this paper I have detected on the south-east flank of the Wrekin, 

 near the cottage, one good specimen of a worm-burrow, apparently 



