J. E. Marr—The SIciddaW Slates. 127 



leaden-grey gritty shales, and these shales are probably restricted 

 to some definite horizon in the Tetragraptus Beds, but we have no 

 evidence as to the exact position of that horizon. The further 

 occurrence of Azygograptus in the Ellergill Beds suggests a fairly 

 high position for the grits with Azygograptus La^noorthi. 



Black shales with Didymograptus indentus, var. nanus, in profusion 

 form a marked feature of these beds. They are often traceable for 

 a considerable distance along the line of strike. The presence of 

 these tuning-fork Didymograpti, which are elsewhere so character- 

 istic of Upper Arenig and Lower Llandeilo strata, indicates that the 

 Didymograptus nanus Beds form the upper division of the Tetra- 

 graptus Beds, which may, therefore, be divided into (1) Lower 

 Tetragraptus Beds and (2) Upper Tetragraptus Beds, with abundance 

 of Didymograptus nanus. An examination of the Graptolites associ- 

 ated with Didymograptus nanus near Mungrisdale bears out this view. 



The Tetragraptus Beds and the overlying Ellergill Beds contain 

 the greatest number of Trilobites hitherto discovered in the 

 Skiddaw Slates. Most of these Trilobites belong to the " Llanvirn " 

 fauna. I hope to refer to them at greater length in another 

 communication. 



3. Ellergill Beds. 



These beds are usually recognizable with ease by their peculiar 

 earthy nature. Their fauna is also different from that of the under- 

 lying rocks, and indicates a very high position in the Arenig Series. 

 They are typically developed at Ellergill, Knock Ore Gill, and 

 Ashlock Sike in the Cross Fell Area, at Thornship and Keld Becks 

 near Shap, and in the moory country near Troutbeck Station, 

 extending towards Threlkeld. Amongst the Graptolites which 

 have been found in these beds are : — 



Didymograptus affiins, Nich. 

 ,, bifidiis. Hall, 



,, indentus, var. nanus, Lapw. 



,, Miirchisoni, Beck. 



t ,, fasciculatus, Nich. 



,, Nicholsoni, Lapw. 



t Azygograptus Calebs, Lapw. 

 t Trichograptus gracilis, Nich. 

 Phyllograptus an gust if alius. Hall. 

 Diplograptus dentatus, Hall. 

 Glimacograptus . 



Cryptoyraptus ? Hoplcinsoni, Lapw. 

 ,, tricornis, Carr. 



t Glossngraptus armatus, Nich. 

 f Trigonograptus ensiformis, Hall, 

 t ,, lanceolatus, Nich. 



Those marked f have hitherto been found only in this division of the Skiddaw 

 Slates. 



4. MiLBUKN Beds. 



Mr. Goodchild has applied this name to certain slates interstrati- 

 fied with volcanic rocks, which in the Cross Fell area appear to 

 form a passage between the Skiddaw Slates and the volcanic series 

 of Borrowdale, Similar beds occur in many parts of the Lake 



