400 Prof. Sedgwick on the New Red Sandstone Series in the 



Pontesford towards Westbury, and surmounted by a series of deposits con- 

 nected with the group of the new red sandstone. The order of succession, 

 as laid bare by a deep cut for the road near Aldbury, is as follows : 1st, Coal 

 measures. 2ndly, Coarse reddish sandstone^ in character intermediate between 

 a coarse coal grit and a true red or variegated sandstone. 3rdly, A very fine 

 magnesian conglomerate^ forming a distinct range of hills by Cardeston^ 

 Rownton^ and Adenbury, and in mineral structure like the Bristol and De- 

 vonshire conglomerates*. 4thly, Red and variegated sandstone descending 

 into the great plain of Shropshire^ and of unknown thickness. Here, there- 

 fore, the section is more complete than at Bristol, and is perfectly analogous 

 to the Cumberland coast section, with this exception, that the conglomerate 

 is developed at the entire expense of the magnesian limestone. The con- 

 clusion naturally deduced from this section is the same as that at which I 

 before arrived — viz. that the magnesian conglomerates do not represent the 

 rothe todte liegende, but a part of the next superior division — the magnesian 

 limestone, or zechstcin. 



In comparing the Bristol and Exeter conglomerates with the rothe todte 

 liegende, our geologists made use of the best evidence with which they were 

 acquainted. But the new red sandstone group is now better understood ; and 

 in future comparisons with Continental deposits of the same age, we should 

 use, as our types, those sections which are most complete, instead of the Bristol 

 or Exeter overlying groups, in which more than one half the series is abso- 

 lutely wanting. Nor is any assistance to be derived from the accidental pre- 

 sence of porphyry pebbles ; in as much as they occur in the Shropshire con- 

 glomerates, as well as in those of Exeter, and are in truth of no value in de- 

 termining the relative age of any secondary rock. 



It must, however, be allowed that a considerable part of our difficulties have 

 arisen from the ill-defined language of some of the German geologists. The 

 term rothe todte liegende has probably been often applied to conglomerates of 

 the same age with our magnesian conglomerates. It originally designated 

 certain, coarse, red sandstones overlying the coal measures of the Hartz, which, 

 after a personal examination of them, I believe to be the exact equivalents of 

 the 'Mower red sandstone" above described. In the late works of Mr. Hoff- 

 mann the same term is applied to a red sandstone under the coal measures of 

 Wettin, and therefore on the parallel either of some of our lowest red coal 

 grits, or perhaps of our old red sandstone. 



* The condition of the pebbles imbedded in this conglomerate is very remarkable. Some of 

 the mountain limestone pebbles retain their mineral structure and characteristic fossils ; others are 

 so altered as hardly to be distinguishable ; some having become granular, and some perfectly pul- 

 verulent. See a previous note, p. 390. 



