18 PROF. E. J. GARWOOD AND MISS E. GOODYEAR [vol. lxxiv, 



striking reef-like development of bryozoa, the mass of the reef 

 being composed of branches of Coenites repens, a form especially 

 characteristic of the Upper Silurian of Gotland and also of Russia 

 and North America. 1 This form includes the two species C. jani- 

 perinus and C. intertextus mentioned in Murchison's ' Siluria.' 

 The branches are frequently encrusted with growths of calcareous 

 algse, notably Spkarocodmm gotlaiidicu mJ&othipletz (PL VI, fig. 3). 

 This organism appears in thin sections under the microscope, in 

 the form of chain-like growths having two distinct forms of cell. 

 The smaller of these have an average diameter of 29 fx, while in 

 the larger form of cell- the diameter may exceed 300 fx. Many 

 of the sections show the digitated expansions characteristic of the 

 genus (PI. VI, fig. 4). This lower bryozoa-bed is well exposed 

 beside the path running along the south-eastern margin of the 

 inlier, immediately south of the stile and close to Weythel Brook, 

 and again in the floor of Dolyhir Quarry, and also in the old 

 quarry opposite containing the railway-siding. Associated with 

 this lower bryozoan reef occurs a band characterized by the abun- 

 dance of the large brachiopod Stroplieodonta semiglohosa. 



Near the summit of the limestone we find another conspicuous 

 development of bryozoa. In this case it is associated with 

 abundant remains of Favosites and Holy sites, and is succeeded 

 by a compact band, a few inches thick, containing numerous 

 specimens of Orthoceras, belonging to three species, of which 

 the large form O. angulatum, with its characteristic reticulate 

 surface, is the most conspicuous ; with it occurs O. excentricum, 

 which was originally figured by Murchison from the Old Radnor 

 limestone. A good exposure of this Orthoceras bed was until 

 recently visible at the summit of the western end of Strinds 

 Quarry, but this has now been almost entirely quarried away. 



(d) The Included Shale-Band. 



Though the mass of the Woolhope deposit is essentially calca- 

 reous, traces of a thin shale-band are found in several of the 

 sections. Everywhere, where it is present, the shale has formed a 

 line of weakness along which movement has taken place, so that it 

 cannot be traced continuously for more than a short distance ; 

 wisps of it may, however, sometimes be seen, caught up and teased 

 out along the thrust-planes. As a result of this the shale does not, 

 at first sight, appear to occur at any definite horizon in the lime- 

 stone, and might easily be mistaken for a fine layer of crushed 

 rock, developed along lines of movement. A careful study, how- 

 ever, of the shale shows that it is definitely confined in all the ex- 

 posures to the horizon of the lowest biyozoa-bed and the associated 

 Stropheodonta band, near the base of the succession. It is well 



1 A. Hennig, ' Gotlands Silur-Bryozoer : II ' Arkiv for Zoologi, K. Svensk. 

 Vetensk. Akad. vol. iii, No. 10 (1906) p. 27. 



