and the Palceozoic System of England. 303 



sandstone *. I may further state, that during two short visits 

 to the Onny section, made by my friend John Ruthven and 

 myself, in the summers of 1846 and 1851, for the sole purpose 

 of collecting fossils, we did not find a single characteristic Cara- 

 doc species over the Hollies limestone. The state of the river 

 had on both occasions been very unfavourable to our examination 

 of the shales near Stretford Bridge ; but my friend Mr. Duppa, 

 of Cheney Longville, promised (in 1851) to make excavations 

 among them, in places where they were out of the reach of the 

 waters. He has since then amply performed his promise, and 

 his excavations have not laid bare any characteristic Caradoc 

 species in the shales immediately above the bridge. I therefore 

 now accept a suggestion (more than once made by Mr. Salter 

 and Prof. M^Coy), that, in my note-book of 1842, 1 had mistaken 

 Stretford Bridge for another bridge further up the Onny ; and 

 in this way the section of the Onny is no longer (as it will ap- 

 pear in the sequel) in any real antagonism with the sections of 

 May Hill and the Malverns. 



These preliminary remarks will sufficiently explain the pur- 

 pose of our short visit, made near the end of August (1853), to the 

 frontiers of Wales and Siluria. 



My first intention was to re-examine (during the early part of 

 last summer) the grits, conglomerates, and shelly sandstones 

 which range from Conway to the neighbourhood of Corwen, and 

 form the base of the Denbigh flagstone : and I may remark, by 

 the way, that these important beds had been carefully laid down 

 in 1843 by Mr. Salter and myself, and were at that time con- 

 sidered and coloured as Upper Silurian. After having effected 

 this first purpose, I hoped to follow the same grits and sand- 

 stone in their range along the Berwyn chain ; and lastly to fol- 

 low them, as they are laid down (I doubt not with great accu- 

 racy) in the Government Map, until they finally thin out and 

 disappear. 



I believe that, with very limited exceptions, the whole '^ Middle 

 Silurian " group of the Government Map is the exact equivalent 

 of the "May Hill sandstone.'^ The conglomerates, grits, and 

 sandstones above mentioned are unconformable to the Cambrian 

 rocks on which they rest, in their range from Conway to Corwen, 

 and, in that part of their range, are the undoubted equivalents 

 of the May Hill sandstone. That they are unconformable to the 

 Cambrian rocks on which they rest, in a part of the Berwyn 

 range, is also, I think, evident ; for they appear as the highest 

 beds of a trough, on both sides of which there is an outcrop of 



* I stated this hypothetical conclusion in a letter to my friend Mr. Salter 

 before he commenced his re-examination of the Horderley and Wenlock 

 sections in 1853. 



