Vol. 56.] SHALES OF THE WELSH BORDERLAND. 413 



whom I am indebted for the drawings of the graptolites figured 

 in the plate attached to this paper. 



EXPLANATION OF PLATE XXIY. 



[All the figures are of the natural size.] 



Fig. 1 a. Cyrtograptus Lundgreni, Tullb. River Irfon. Coll. G. L. Elles. 

 1 b. ft Lundgreni, Tullb. Llwynrhedith Quarry. Coll. G. L. Elles. 

 Figs. 2 a & 2 c.« Cyrtograptus rigidus, Tullb. Dulas Brook. Coll. Gr. L. Elles. 

 Fig. 2 b. ft rigidus, Tullb. River lrfon. Coll. G. L. Elles. 



3 a. Cyrtograptus Linnarssoni, Lapw. Builth Road. Coll. C. Lapworth. 



(Type-specimen, re-figured by kind permission of Prof. Lapworth.) 



4 A. Cyrtograptus symmetricus, sp. nov. Coed Mawr. Coll. G. L. Elles. 

 4 b. ft symmetricus, sp. nov. Near Castle Crab. Coll. G. L. Elles. 



Figs. 5 & 5 a. Monograptus riccartonensis, Lapw. Walcot. Coll. G. L. Elles. 

 Fig. 6. Cyrtograptus Murchisoni, Carr. Pencerrig. Woodwardian Museum. 



Discussion. 



Prof. C. Lapworth pointed out the extreme interest of this paper, 

 both from the stratigraphical and from the palaeontological point of 

 view. The zonal mapping of the Welsh Silurians commenced by 

 Prof. Watts, carried through the Bhayader Yalentian by Mr. Herbert 

 Lapworth, had here been brought out in detail stage by stage through 

 the Wenlocks of the Welsh Border by the Authoress. In a forth- 

 coming paper by Miss Wood, it would be found to be extended to 

 the summit of the Lower Ludlow. The wide-spreading sheets 

 of Silurian strata of similar lithological character, necessarily left 

 unbroken all in one colour by the earlier geological surveyors, 

 would, in the not far distant future, be found banded zone by zone 

 upon our maps in as great detail as the Lias or the Oolites. The 

 excellent map of the Builth district submitted by the Authoress was 

 a type of what these maps will be. 



It has long been known that the Silurian was a period of slow 

 and long-continued depression, and subsequent slow upheaval. In 

 these zonal lines on our maps we are now beginning to watch the 

 stages of this general movement and its local interruption by crust- 

 creep. It is most satisfactory to find that the discoveries of the 

 Authoress confirm the views and discoveries of the late Dr. Tullberg, 

 and show (with one exception) that his arrangement of the Scandi- 

 navian zones holds good also for the British Wenlock deposits. 



With regard to the palseontological bearings of the paper, it 

 touched upon the fringe of a difficult subject, of which, notwith- 

 standing the publication of the suggestive papers of Prof. Nicholson 

 and Mr. Marr and the Authoress, we as yet know but little. The 

 classification of fossil-remains by form, and the classification by 

 presumed descent, have yet to be harmonized. The eidographic 

 grouping, or classification by form, and the phylogenetic 

 grouping, or classification by descent, have both their uses. It has 

 long been known that graptolites, as well as other organisms, were 



Q. J. G. S. No. 222. 2 p 



