482 ReV' J. F. Blake — Precamhrian Geology. 



Actinoceras sulcatulum and Solenoeheilus latiseptatus are common 

 in the Ceraent-stone (Upper division of the Carboniferous Limestone) 

 of the West of Scotland. I have myself collected them in the 

 Arden Quarry, at Nitshill, near Glasgow (see Cat. Foss. Ceph. Brit. 

 Mus. (Nat. Hist.), pt. i. 1888, Suppl. p. 319). 



The present species has been vv^ell described, but poorly figured 

 by Armstrong (Trans. Geol. Soc. Glasgow^, vol. ii. pt. i. ,p. 74, pi. i. 

 figs. 6-7) under the name of Nautilus (Discites) nodiferus. Its 

 identity with Romer's species is, however, beyond question. 



The following is Armstrong's description : — " Shell discoidal, 

 composed of about three gradually enlarging, contiguous, nearly 

 subquadrate whorls, completely exposed in a moderately shallow 

 umbilicus; back broad, rounded at the edges, and traversed in the 

 middle by a wide and deep channel, on the sloping sides of which 

 are two fine thread-like ridges. The remainder of the space on 

 the back and sides of the shell is occupied by six rows of closely 

 set, prominent, obtuse tubercles, elongated in the direction of the 

 aperture, one row of tubercles of large size bounding the back, a 

 double row of equal size between it and the channel, and three on 

 the sides, which decrease in size towards the umbilicus. Surface 

 marked with coarse, squamose, wavy lines of growth, which are 

 arched backwards in the dorsal [=:ventral, or peripheral] channel. 

 Septa numerous, their edges arched considerably backwards on the 

 periphery, and slightly so at the sides. Siphuncle -iV inch diameter, 

 central. Dimensions — width of greatest diameter 3J inches, width 

 of outer whorl near the aperture, 1 inch." 



The specimen presented by Mr. Seward is a valuable accession to 

 the British Museum collection, which hitherto possessed only some 

 small fragments of this beautiful species. These are described in 

 part ii. of the Catalogue of Fossil Cephalopoda (1891), p. 139, where 

 also Armstrong's description of the species is quoted. 



II. — On some Eeoent Contributions to Preoambrian Geology. 

 By J. F. Blake, M.A., F.G.S. 



THE last two numbers of the Quarterly Journal of the Geological 

 Society contain three communications concerning rocks which 

 are, or are thought to be, Precamhrian. Two of them are in direct 

 attack on work of mine, and the third incidentally opposes some 

 portion of it. The materials of any reply I may have to make are, 

 for the most part, already published in my papers, but the bearing 

 of these facts seems to require to be pointed out. 



Taking the communications in order, the first is the Anniversary 

 Address of the President. In this he deals, so far as my work is 

 concerned, first with Anglesey. Sir A. Geikie states that he was 

 not prepared by previous writings for certain results he obtained. 

 He was much astonished to find in central Anglesey so striking a 

 counterpart to portions of the old gneiss of the north-west of Suther- 

 land and Eoss. Speaking of the rocks which he here refers to, I 

 wrote, " I'he question is suggested whether we may not touch here a 



