194 a. D. Roberts — On the Tu't Hill Conglomerate, Carnarvon. 



to place this large head-shield with others in the sub-genus 

 Zenaspis, on the ground that with it have been found associated 

 some remarkable scutes which are regular in size and hemispherical 

 in outline. These scutes are symmetrical in outline, and were 

 probably placed in the median line on the dorsal surface. They 

 indicate an armature of body quite different from that of C. Lyelli. 

 The flank-scales of individuals as large as Mr. J. E. Lee's specimen 

 must have been of considerable size and strength. 



We are indebted to Mr. J. E. Lee for kindly permitting us to 

 reproduce the plate of this fine fossil in the Geological Magazine. 



IL — Evidence bearing upon the Position of the Twt Hill 



Conglomerate. 



By R. D. Roberts, M.A., D.Sc. (Lond.), F.G.S., Clare College, Cambridge. 



A DISCUSSION has more than once arisen, in the course of the 

 last two years, respecting the true position of the quartz 

 conglomerate exposed near Twt Hill, Carnarvon, which was first 

 described by Prof. Bonney and Mr. Houghton in the Quarterly 

 Journal of the Geological Society, vol. xxxv. p. 321. The typical 

 quarry is situated on the S.E. side of the ridge, close underneath 

 Twt Hill, and the exposure there shows the quartz conglomerate in 

 juxtaposition to the granitoid rock that constitutes the axis of the 

 ridge. The authors describe a passage between the granitoidite 

 below and the conglomerate above, and state that the latter " passes 

 up into a rock which has some resemblance to the bottom rock " 

 (granitoidite). In the Geol. Mag. for March, 1880, p. 118, Dr. 

 Callaway writes: "Messrs. Jionney and Houghton have detected at 

 Twt Hill a passage between the granitoidite and a quartzose con- 

 glomerate with a S.E. dip. I have visited this section, and having 

 examined the rock inch by inch, I can entirely confirm their identi- 

 fication." 



Fig. 1. (Ground Plan of Twt Hill Quarry). 



a. Granitoid Rock of Twt Hill. c. (Sandstone. 



b. Quartz Conglomerate. /. Small Faults. 



To this view of the position of the quartz conglomerate as a 

 part of the lowest Pre-Cambrian series, Prof. Hughes took ex- 

 ception ; a careful study of the stratigraphical relations of the 



