538 Geological Society. 



formation, and occurs in vast numbers in a bed which forms about 

 the middle of the Ludlow series. Mr. Murchison has told us that 

 this little shell is usually found in such numbers as to form a bed 

 which lies above the Aymestry limestone, and it serves to mark the 

 place of that rock where it is wanting : and Mr. J. E. Davis informed 

 the author, that at Stapleton, near Presteign, where there is no 

 Aymestry limestone, this species is found throughout the whole of 

 the Lower Ludlow shales. Mr. Sharpe has made use of this shell 

 in dividing the Upper from the Lower Ludlow rocks in Westmore- 

 land, classing all the beds containing it in the lower series. The 

 bed in which it occurs in greatest abundance was traced through 

 Underbarrow, by Tullithwaite Hall and High Cray, across the west 

 end of Rather Heath and a little south of Cowan Head, and also in 

 Lambrigg Park ; it is usually accompanied by Atrypu affinis, Spirifer 

 octoplicatus, Leptozna lata and depressa, Orthis lunata, and Terebratula 

 nucula : the T. navicula seems to have died out -suddenly, as it is not 

 found in the Upper Ludlow beds. 



The same division of the Ludlow rocks may be obtained by attend- 

 ing to the direction and dip of the beds ; the lower series partakes 

 of the north-east strike, which runs through the older Silurian rocks 

 in these counties, and is traversed by many of the same faults as 

 those formations, but the Upper Ludlow beds are thrown up in anti- 

 clinal ridges with a different direction. 



Mr. Sharpe gives a list of the organic remains found in each divi- 

 sion of the formation, which includes forty-four of the species de- 

 scribed in Mr. Murchison's work from the old red sandstone and 

 Upper Ludlow, fourteen of those from the Aymestry limestone, and 

 twenty-two of those from the Lower Ludlow beds. Of the species 

 of shells placed by Mr. Murchison in the old red sandstone*, all 

 but two have now been found low in the Ludlow beds, proving that 

 the red beds containing these species in Herefordshire must be elassed 

 with the Upper Ludlow formation. 



Old Red Sandstone. — The only addition to the former paper which 

 relates to this formation, is in mapping it in the upper valley of the 

 Lune, where the tile-stones reach above the hamlet of Langdale, 

 dipping N.N.E. 10°. 



The age of the large masses of gravel of a brown or red colour 

 noticed in the valley of the Lune between Sedberg and Casterton, 

 and of the Kent and Sprint, was before left uncertain ; the author 

 now regards them as a modern surface drift. 



Mountain Limestone. — The description of this formation did not 

 enter into Mr. Sharpe's plan, but he examined the portion of it which 

 occurs in Low Furness, to ascertain the geological position of the 

 Ulverston iron ore. 



The ore occurs in veins usually perpendicular, and bearing 

 W.N.W., which cut through the limestone, but are not continued 

 into the Silurian rocks. The following veins are mentioned : — 



Plumpton Hall ; now abandoned. 



Lindal Moor vein ; an exception to the usual condition, as it runs 

 between the mountain limestone and the Windermere grits, striking 

 * Silurian System, p. 603. and t. 3. 



