DESCRIPTION OF THE MAP. 



xxix 



Of the demarcations of the Old Red and Silurian Systems, it is unnecessary that I should now 

 speak, as they are so fully treated of in the work ; yet as these parts of the map are more especially 

 illustrated by myself, I crave the indulgence of those who may follow me ; begging them to consider, 

 not merely how little the region had been previously explored, but also how much aid the geologist 

 is deprived of in a tract where there are few mines or underground operations 1 . Still I venture to 

 hope that this map may serve as an auxiliary to the illustration of the Ordnance Maps which is 

 proceeding under the direction of M. De la Beche, and I trust that my labours will aid him in 

 laying down the outlines of the various groups of rock in this region ; though there can be no doubt 

 that the details may be much improved by the discoveries of himself and his assistants. 



It now remains for me to express my thanks to those friends who have aided me. Professor 

 Sedsrwick determined the outline between the Silurian and Cambrian Rocks, from the Berwyn moun- 

 tain northwards. (See Map.) Mr. Lonsdale defined the course of the oolite and lias of the Cottes- 

 wold Hills. Mr. H. E. Strickland traced the boundary between the lias and red marl, as well as 

 the line of the Keuper Sandstone throughout a large part of Worcestershire. The Rev. T. Egerton 

 assisted me in laying down the boundary of the lias of North Salop. Mr. F. Downing enabled me 

 to trace the boundary of the 10 yard coal-field of Dudley; Mr. Prestwich's map of the coal-field 

 of Coal Brook Dale has been highly serviceable, as well as that of the coal-basin of the forest of 

 Dean and adjacent country, by Mr. Maclauchlan ; Sir Philip de Grey Egerton indicated the boun- 

 dary of a small coal tract in North Staffordshire, and Mr. Bowman determined the outline of the 

 Denbighshire coal-field. In the other coal-fields I have chiefly depended upon my own observa- 

 tions. I must further state, that after my map was engraved, an important improvement in the 

 outline of the Carboniferous Limestone on the western flank of the south Welch coal-basin was 

 kindly inserted by Mr. W. E. Logan, (see the transverse faults east of Llandovery and Llandeilo,) 

 who with great perseverance and ability had, unknown to me, laid down upon the Ordnance Map 

 many details and remarkable dislocations of the Glamorganshire basin, the northern, eastern, 

 and western boundaries of which are all that I allude to 2 . 



I have to thank Colonel Colby, Lieut. -Colonel Mudge, and Major Robe employed on the Tri- 

 gonometrical Survey, for their ready compliance with my wishes, in furnishing me with outlines 

 of tracts, the sheets of which were not published when I commenced my researches, and I am 

 also much obliged to Mr. Maclauchlan and Mr. Budgen, Ordnance Surveyors ; to the former for 

 much geological, the latter for some local valuable topographical data. The reduction, engraving 



Sandstone or the Keuper ; 2nd, the Red Sandstone or Bunter Sandstein ; and, 3rd, the Lower New Red or 

 Rothe-todte-liegende, and wherever the two last-mentioned formations are known to be separated by the cal- 

 careous conglomerate or equivalent of the Magnesian Limestone, its course is indicated by a green stripe. In 

 a note, p. 66, printed before I decided upon the extent to which the subdivision of colours could be applied to 

 the map, it is stated that two tints of red only are employed in illustrating the New Red System. 



1 Although no one had pointed out the subdivisions of the older rocks near Ludlow, I am bound to state that 

 Messrs. R. and W. Wright of the Ordnance Survey, have laid down very correctly the general outline of the 

 Ludlow promontory in a map presented to the Geological Society. 



2 By reference to p. 165, printed a year-and-a-half before I became acquainted with the observations of 

 Mr. Logan, it will be perceived that I had noticed the great transverse dislocations near the Caermarthen Fans 

 in my earliest visits to South Wales 1832-3. I had not, however, laid them down with that precision which 

 marks the field work of Mr. Logan. 



