214 EXPLANATION OF THE CLAXHEUGH SECTION. 



LITERATURE. 



The section has been noticed by various authors. Sedgwick, 

 in his classical paper on the " Internal Structure of the 

 Magnesian Limestone," mentions it and gives a section of 

 it (i). Howse, in "Notes on the Permian System of North- 

 umberland and Durham," says, of the Shell Limestone, 

 "When seen in section it generally rests on the Compact 

 Limestone, but at Clack's Heugh it rests on a bed of friable 

 sandstone" (2); and, again, in a "Catalogue of the Fossils of 

 the Permian System," he writes, "In a few localities as at 

 Clack's Heugh on the Wear, the Marl Slate is entirely absent, 

 and the lowest bed of limestone, which is seen in one part of 

 the section resting on the sandstone is very thin and earthly "(3). 

 Kirkby also refers to it in a paper on " Fossils of the Marl 

 Slate and Lower Magnesian Limestone "(4). Professors King 

 and Lebour also notice the section. The latter geologist in 

 his " Geology of Northumberland and Durham," gives a 

 section showing the junction between the Yellow Sands and 

 overlying rocks as seen at Claxheugh in 1884(5), ^^^ says, 

 "Were it not for the interesting group of organic remains 

 found in the Marl Slate, it would no doubt be properly re- 

 garded as merely a subordinate member of the limestone, 

 although occasionally there are distinct lines of unconformity 

 between the two. This is notably the case at Claxheugh, 

 where a splendid section is exposed on the south bank of the 

 Wear about two miles above Sunderland. Clear as the fact 

 is that here, the Marl Slate was disturbed and denuded before 

 the deposition of the Magnesian Limestone on it, the uncon- 

 formity is probably only a local one with no general signi- 

 ficance" (6). 



DESCRIPTION OF SECTION. 



The manner in which the Marl Slate and Compact Lime- 

 stone terminate is shown in Section I. It will be seen that 

 these two beds are present at the western end but absent from 

 the eastern, and the manner in which they end is complicated 

 and peculiar. This can perhaps be only properly realised by 



