and the Palaozoic System of England. 307 



II. Pentamerus beds of Norbury and Linley^, 



The extension of these beds along the southern edge of the 

 Longmynd chain, upon which they rest unconformably, has been 

 well known to geologists since the publication of the ^ Silurian 

 System/ In Siluria they were discovered, and there they have 

 their best, and perhaps their only unequivocal type. Their 

 thickness is not great, and at Linley and Norbury the thickness 

 might, on a superficial view, be easily overrated, inasmuch as 

 the beds dip very nearly with the inclination of the ground, and 

 therefore are spread over a considerable surface. It would be 

 idle for me to attempt any detailed description of these well- 

 known beds; but I may just remark, — (1) That some of the 

 lowest beds are very irregular, coarse, and of mechanical struc- 

 ture, and with very few traces of fossils. (2) That over the 

 above are five or six feet of a bluish-gray ragstone : the beds 

 with very uneven upper and lower surfaces, separated by semi- 

 indurated wayboards, marked by many ferruginous stains, and 

 with a few casts of fossils. (3) That higher in the section are 

 five or six feet of gray and yellowish-gray beds, slightly ferrugi- 

 nous, and with many cellular streaks marking the presence of 

 fossil casts ; also bands of ferruginous " rotten-stone," with in- 

 numerable casts of fossils. As usual, the calcareous matter had 

 quite disappeared from the "rotten-stone" bands. (4) That 

 over the above comes the well-known and beautiful Pentamerus 

 (or Norbury) limestone.' This limestone is, in the Norbury 

 quarries, extensively worked for the neighbouring hme-kilns. 

 The beds are very irregularly deposited, but their average thick- 

 ness is about five or six feet. The preceding group plunges 

 under the soil, and no higher beds were seen ; but there seems 

 to be no doubt that it is almost immediately overlaid (as repre- 

 sented in our best maps) by the Wenlock shale. These facts 

 would not be worth noticing, did they not serve to give a con- 

 nected meaning to the following account of the fossils we found 

 in the quarries of Linley and Norbury. 



Ceiriog, and also in several sections near the road from Llangollen to 

 Ruthin), which I have often called the paste-rock, are very nearly at the 

 crown of the whole Cambrian series. They were in 1843 sometimes 

 regarded as " beds of passage " by my friend Mr. Salter and myself. They 

 were not, however, true beds of passage in the places where we saw them, 

 as they were overlaid by the Wenlock shales, without the intervention of 

 the May Hill sandstone. 



* This small group is an important member of the palaeozoic system, and 

 it deserves a geographical name. It may (from its best locality) be con- 

 veniently called Norbury limestone. " Pentamerus limestone " is a bad 

 name for this small group ; for a Pentamerus (though of a different species) 

 is also characteristic of another limestone — the Aymestry. 



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