and the Palceosoic System of England, 4^ 



from his Lower Silurian groups. The Bala limestone must 

 therefore (if the Lower Silurian sections were right) be put in 

 a lower system than that of Glyn Ceiriog. This threw my 

 Upper Cambrian sections into great confusion ; for it is only by 

 a distortion of the Geological Map that the Ceiriog limestone 

 can be thrown out of co-ordination with that of Bala. An error^ 

 and a great error there was ; and it must have arisen from some 

 great mistake, either in my Upper Cambrian, or my friend's 

 Lower Silurian, sections. I provisionally accepted the former 

 alternative, greatly to my own cost ; for it led me inevitably into 

 errors in the estimate of the older rocks of the north of England^ 

 by putting before me what I afterwards knew to be an erroneous 

 Silurian type*. So far from the '' Lower Silurian^' groups being 

 a key to unlock the mysteries of our older palaeozoic rocks, they 

 became a bolt to close the door of progress. 



On my next return to North Wales in 18*42, I found that all 

 my Upper Cambrian sections had been true to nature j but a 

 mistake there was as I could prove to demonstration, and that 

 mistake must now, therefore, be attributed to the right quarter, 

 — to a great mistake in the original Silurian sections. 



What took place afterwards needs no long comment. My 

 Upper Cambrian groups (which I have since extended downwards 

 to the flank of the Arenig porphyries as in the Tabular View) be- 

 came interlaced, as I had suspected in 1833, with the Lower Silu- 

 rian; and all the entanglement which afterwards arose sprang from 

 no mistake whatsoever in my Upper Cambrian sections, but from a 

 great mistake in the Lower Silurian. I therefore proposed a com- 

 promise^ viz. that all the groups from the Bala limestone to the 

 base of the Wenlock shale should be called Cambro- Silurian. 

 I had placed those groups correctly in the great Cambrian 

 series, but had said little of the fossils ) except that, so far as I 



* Should any one thirik it strange and almost incredible that I should 

 thus have distorted my own sections tp bring them into accordance with 

 the Lower Silurian scheme {supra, fig. 5. p. 313), let him bear in mind 

 (1) that the Glyn Ceiriog calcareous slates are immediately overlaid by the 

 Wenlock group, and that the Bala limestone and its calcareous slates 

 are overlaid by several thousand feet of strata bearing neither physical 

 nor fossil analogy to the Wenlock group. (2), That on this sectional 

 ground the Upper Bala group was also separated from those of Glyn 

 Ceiriog and Meifod ^ y the author of the ' Silurian System." (3). That 

 there is a true Silurian group to the west of Corwen and on the line of the 

 Holyhead road. Which is based on the May Hill sandstone. What 1 sup- 

 posed in 1834 (when I for the last time parted from Sir R. I. Murchison 

 in North Wales) was this, viz. that the Glyn Ceiriog limestone might be 

 prolonged to the base and made a part of the group I now call May Hill 

 sandstone. It was an hypothesis to which I was absolutely driven, pro- 

 vided the Lower Silurian sections were, as I then beheved, perfectly true 

 to nature. I had no time that summer to test the hypothesis. 



