54 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 16, 



for a coarse kind of roofing-slate. The strata are tMn and very re- 

 gular, and dip at 65° to N. 51° W. of true direction. No cleavage 

 appears in these beds, and the slates are formed by splitting the mass 

 along the laminae of deposition, as the position of the fossils clearly 

 proves. The rock is intersected by two sets of open fissures, of which 

 one series dip at 85° to W. 45° S. ; and another at the same angle 

 to E. 5° N. The amount of dip and the direction vary considerably 

 in both, the second being more irregular ; the edges of the beds along 

 it are also broken, rubbed and striated, as if the masses of slate had 

 been pushed over each other. The surfaces of some of the beds are 

 very curiously marked, as the specimens on the table will show. Some 

 of these resemble the ripple-mark common on sandstones, and others 

 are not unlike the impression of some organic body, but the whole are 

 more probably concretionary and entirely mineral in character. In 

 some beds, concretions partly calcareous, partly ferruginous occur, 

 the latter much resembling moss or decaying wood, but showing no 

 trace of organization when examined by the microscope. A few feet 

 above these graptolite beds there is a thin irregular layer from half 

 an inch to two inches thick, of a granular rock containing fragments 

 of steatite and mica of a pinchbeck brown colour. 



In this quarry at least two beds containing fossils occur. The 

 upper one is a fine-grained greywacke, the surface of which is almost 

 covered by the Graptolites Sedgivickii, but the specimens, from the 

 nature of the stone, are rarely well-preserved. About ten feet lower a 

 bed of slate has been lately opened containing fossils of this genus in 

 great abundance, which are found not only on the surface, but also 

 through a considerable thickness of the slate. This circumstance, taken 

 in connexion with the finer materials of the matrix and the beautiful 

 state of preservation of the imbedded fossils, shows that these have 

 Hved on the spot, whereas those in the higher bed have more probably 

 been drifted to this place by a stronger current. About seventy to 

 eighty feet higher a third bed containing graptolites is known, but 

 as a slip intervenes, it may probably be one of those already mentioned. 

 At least six species of graptolites occur in this locality, as enumerated 

 in the following list : — 



Graptolites Sedgwickii, PortlocJc. Graptolites convolutus, Hisinger. 



distans, PortlocJc. — — ludensis, MurcMson. 



tenuis, PortlocJc. griestoniensis, new species. 



The last seems very distinct from any species formerly described, 

 and is well-characterized by the oblong form of its polyp-cells which 

 are closely appressed to the axis. The first four of these species were 

 found by Colonel Portlock in the Lower Silurian slates of Desertcreat 

 in Tyrone ; and the third, G. tenuis, also by Mr. James Hall in the 

 black slates of the Hudson River group of New York, which is con- 

 sidered by Mr. Sharpe and others as the equivalent of the Lower Si- 

 lurian deposits of England. The G. ludensis, though originally dis- 

 covered by Sir Roderick Murchison* in a higher part of the series, 

 extends down mto the Llandeilo flags. The G. convolutus, first de- 

 scribed by Hisinger from the clay-slates of Sweden, has been since 

 * Siluiian System, p. 694, pi. xxvi. fig. 1, la.- 



Y 



