W. T. Aveline — Silurian Strata of the Lake District. 441 



EXPLANATION OF PLATE X. 



Figs. 1 and 2. Hemiaspis Umuloides, H. "Woodw. Lower Ludlow, Leintwardiae. 



Fig. 1 from the Museum of Practical Geology, Jermyn St. ; Fig. 2 from 



the British Museum. 

 Fig. 3. Fragment of head-shield of Hemiaspis. 



Fig. 4. Hemiaspis Sahveyi, Salter. Lower Ludlow, Ledbury. Coll. Mus. Brit. 

 Figs. 5 and 7. S. speratus, H. "Woodw. Lower Ludlow, Leintwardme. Coll. 



Mus. Brit. 

 Fig. 6. Hemiaspis horridus, H. Woodw. "Wenlock Shale, Dudley. Coll. Mus. Brit. 

 Fig. 8. Bellinurus Kbnigiajvus, H. "Woodw. Coal-Measures, Dudley Coal-field. 



Coll. Mus. Brit. 

 Figs. 9 and 10. Prestwichia BirtwelK, H. "Woodw. Coal-Measures, Cornfield Pit, 



near Padiham, Lancashire. Coll. Mr. Thomas Birtwell. 



II, — On the Continuity and Breaks between the various 

 Divisions of the Silurian Strata in the Lake District. 



By "W. Talbot Ayeline, F.G.S., 

 District Surveyor on the Geological Survey of England and "Wales. 



IN a former communication^ I stated that the line of division 

 between the Skiddaw Slates and the overlying Volcanic series 

 (Green Slates and Porphyries), in the neighbourhood of Keswick, 

 was a faulted one, and not an unconformity, as supposed by Mr. 

 Dakyns.- I added that the evidence of an unconformity (if there 

 was one), between these two series of beds, must be sought for 

 elsewhere than in the district described by Mr. Dakyns. Since then 

 I have examined many miles of boundary between these formations, 

 and have as yet only seen one unfaulted junction, and this is near 

 Bootle, in the Black Combe district, Cumberland ; but this section 

 at once sets at rest the question of unconformity or conformity. Not 

 only do the Volcanic series lie at the same inclination with the 

 Skiddaw Slates below them, but beds of the latter alternate with 

 beds of the former, showing a perfect sequence and conformity. 

 When the whole of the boundaries between the Skiddaw Slates and 

 Volcanic series are traced, there may be found other spots also 

 showing conformity and passage. 



The most complete Break in the Lake District is that between 

 the Volcanic series and the overlying Coniston Limestone ; and here 

 we have a considerable unconformity. For when the line of division, 

 between these formations from the Granite at Shap to Black Combe 

 is traced, it will be found that the Coniston Limestone series from 

 lying on the highest known beds of the Volcanic series passes suc- 

 cessively to lower and lower beds, till it finally rests on very low 

 beds in the Black Combe district. So great is this unconformity 

 that sometimes the beds of the Volcanic series strike at right angles 

 to that of the beds of the Coniston Limestone. 



In the Lake District the Coniston Limestone series of beds, which 

 are equivalent to beds on the horizon of the Bala Limestone of 

 North Wales, appear, on a cursory survey, to lie conformably 

 beneath the oveiiying Upper Silurian rocks ; but undoubtedly this 

 is caused by the local accident of the Coniston Limestone series 



1 Geol. Mag., Vol. Nl., p. 382. 2 Geol. Mag.., Vol. VL, p. 56. 



