72 



Mary Anning in the South. The general conclusion of an independ- 

 ent and close observer like Mr. Sharpe cannot but be very gratify- 

 ing to myself; for in stating that in mineral characters these Northern 

 rocks differ most materially from those of Siluria, he points out 

 that in each district the principal divisions of the Silurian system 

 are distinctly maintained. 



Transferring our view from the Lake Region to North Wales, we 

 there find Mr. Sharpe applying the knowledge he had acquired in 

 the Northern districts. In his memoir on the Bala limestone he 

 shows, that, since that rojck and its associated strata contain the same 

 fossils as the Coniston limestone, it is of the Lower Silurian age and 

 not Upper Cambrian, as it was formerly named. He is not however 

 content with merely instancing a similarity of fossils and lithological 

 succession in the Bala rocks, as compared with other well-known 

 Lower Silurian strata, but he also proves by a transverse section, 

 that they occupy a trough, supported on one side by older nonfos- 

 siliferous schists (part of the Berwyns) and on the other by igne- 

 ous rocks (Arran Mowddy). 



I am not prepared to oppose the accuracy of Mr. Sharpe's sec- 

 tion ; but when he quotes me as having stated that the Bala lime- 

 stone dips under the chief mass of the Berwyn mountains, I m.ust 

 be allowed to state, that I visited the locality but on one occasion, 

 with Professor Sedgv/ick, and the limestone beds which I then saw 

 seemed to me to be overlapped by the Berwyn rocks iipon the 

 east. Mr. Shurpe has no doubt accurately examined the whole ter- 

 ritory around Bala, for he states that the limestone, of which there 

 are two bands, is on the whole thrown off from the Berwyns with a 

 westerly dip*, and is again brought up on the edges of Arran 

 Mowdcly with an easterly and south-easterly inclination. In another 

 section, from the head of the lake of Bala to Dinas Mowddy and 

 Mallwyd, he proves that these Lower Silurian rocks, folding over to 

 the east and south, ai'e surmounted by Upper Silurian strata. The 

 whole descending series beneath certain dark blue slates, referred to 

 the lowest part of the Upper Silurian beds, consists of an upper 

 limestone, rotten schist, a second Bala limestone, grey slaty grits, 

 rotten grey clay-slate, and dark blue slate. In all these beds, with 

 the exception of the two lowest, Mr. Sharpe has discovered fossils ; 

 and in addition to well-known British Silurian forms, including the 

 Trinuclei, so characteristic of the Lower Silurian rocks, he has dis- 

 covered the Illcenus crassicauda, a Trilobite, eminently characteristic, 

 I would observe, of the inferior strata of the same age in Scandinavia 

 and Russia. The beds of this group are stated to rest against an 

 unconformable mass of clay-slate forming a portion of the Berwyn 

 chain ; and to this rock, which is void of fossils, and all that lie be- 

 neath it, our author would restrain the application of the word 

 " Cambi-ian." 



This reasoning is clear, but the author must excuse me if I re- 



* Professor Sedgwick still contends that the chief band of Bala limestone 

 dips to the east. 



