Correspondence — Mr. Horace B. Wood /card. 93 



discordance of strike, and that the limestone lies in a synclinal 

 basin, so that its dip in one place is in the opposite direction to that 

 of the quartzite. From the above considerations the author holds 

 that in these districts there is no proof of the Lower Silurian age of 

 the quartzite and newer series of flaggy gneiss and schist. 



3. "On a Boulder of Hornblende-Pikrite near Pen-y-Carnisiog, 

 Anglesey." By Prof. T. G. Bonney, M.A., F.R.S., Sec.G.S. 



The boulder described had been originally about a cubic yard in 

 volume, and the fragments lay in a field left of the road from 

 Pen-y-Carnisiog to Bwlyn. The ground-mass consists of hornblende 

 and serpentinous products with a little mica. In this are crystals, 

 often f inch long, of brown hornblende with inclosures of altered 

 olivine. The author doubted whether this hornblende is not a 

 paramorph after augite; some of that in the ground-mass is certainly 

 of secondary origin. He compared tlie rock with a pikrite from 

 the Lleyn peninsula, and two described by Prof. Geikie from 

 Fifeshire. It differs from all these, but has a singular resendolance 

 to a pikrite from Schriesheim (Odenwald), except that it is rather 

 more altered. He called attention to the rock in hopes that some 

 geologists may discover it in situ, as it will be of much value iu 

 deciding in what direction the ice has moved over Anglesey. 



C O I^I^E S IPO D^IDIE HiTC IE . 



DISTUEBAK'CES IN THE CHALK OF NOEFOLK. 



Sir, — In the " Annals and Magazine of Natural History," for 

 October, 1880, is an interesting paper by Mr. Jukes-Browne on "The 

 Chalk Bluffs of Trimmingham," wherein, after noting the opinions 

 of various writers concerning their origin and history, he expresses 

 his own conviction that they are outlying rocks or needles formed 

 previously to the deposition of the Pliocene (fluvio-marine) series of 

 the Norfolk coast. 



Mr. Jukes-Browne justly compares the disturbances in the chalk 

 at Trimmingham with those at Whitlingham and Swainsthorpe, 

 brought into notice by Mr. J. E. Taylor (Geol. Mag. Vol. II. p. 324 ; 

 Vol. III. p. 44), and endeavours to support his own view of the date 

 of the Trimmingham disturbance by reference to Mr. Taylor's 

 statement that the Chalk at Whitlingham was disarranged before the 

 formation of the Norwich Crag. In a more recent paper by Mr. 

 Taylor (Geol. Mag. Vol. VI. p. 509) the author, however, attributes 

 the twisting and dragging up of the Chalk and its flint-layers to the 

 agent which formed the Upper or Chalky Boulder-clay. This view I 

 entirely coincide with, and during my Geological Survey-work near 

 Norwich I obtained conclusive evidence that the similar disturbance 

 at Trowse was due to glacial action (Geol. Mag. Dec. II. Vol. VI. 

 p. 380). I differ only from Mr. Taylor in assigning the formation 

 of this Boulder-clay to the direct agency of land-ice, whereas he 

 inclines to the view that the Upper Boulder-clay was formed under 

 glacial-marine conditions, and that the stranding of ice-bergs would 

 account for the disturbances of the Chalk. There is much to be said 



