414 J. Prestwich, Esq., on the 



against the flanks of the Wrekin, had been ascertained to be counterparts of 

 others ; but their order of superposition and relative antiquity had not 

 been determined. 



Mr. Murchison's labours, however, have removed these difficulties, by 

 showing, that the thin zones of gray and liver-coloured sandstones, shales, and 

 limestones, which overlie the limestone at Wenlock_, and underlie the coal- 

 measures at Madeley, Broseley, &c., are referable to the Ludlow rocks, the first 

 formation beneath the old red sandstone, and constituting, with the Wenlock 

 limestone and shale, the upper Silurian group ; and that the shelly sandstone 

 at Morrell's Wood, as well as the quartzose grit, and dark-coloured flags at the 

 base of the Wrekin, belong to the Caradoc sandstone, or lower Silurian rocks. 



The deposits just noticed form, in this district, the terminating points of 

 the formations, which having thinned out from their full developement in 

 South Shropshire, Montgomeryshire, Radnorshire, &c., merely constitute, in 

 the neighbourhood of the Wrekin, small and irregular masses, possessing but 

 few of the characters, which distinguish them elsewhere. 



These changes have tended to produce considerable intricacy in the geo- 

 logy of this interesting and beautiful district, where, within a few miles, we 

 find a nearly complete epitome of the carboniferous and Silurian systems. 



I beg leave to acknowledge most particularly Mr. Murchison's kindness, in 

 affording me every assistance respecting the Silurian series. I am also in- 

 debted to that gentleman for the use of a valuable, manuscript Ordnance Map, 

 on which the heights of the principal hills were marked. This document has 

 been of very great service to me in constructing the sections. 



Mr. Arthur Aikin, in his memoir on the Geology of the South-Western 

 part of Shropshire*, gives a general sketch of this portion of the country. To 

 the accuracy and value of the mineralogical details given in that memoir, I can 

 bear ample testimony ; but the extent to which the coal-field was worked at 

 the period of his visit, about twenty years since, was much less than it is now ; 

 and he was consequently prevented from entering into those details, for which 

 his ability and perseverance so well qualified him. 



Dr. Townsonf has given many interesting particulars of the mineralogy 

 of Shropshire; and some notice has likewise been taken of it by the Rev. 

 Mr. Plimley:]:. 



During the whole of my researches, I experienced from all parties much 

 attention and courtesy. To Mr. Anstice, of Madeley, I am particularly in- 

 debted for a constant readiness and kindness in furthering my inquiries. By 



* Geological Transactions, First Series, Vol. i. p. 191 et seq. t Tovvnson's Tracts. 



+ Plimley's Agricultural Survey of Shropshire. 



