Vol. 69.] OF THE COMLEY BRECCIA-BED. 41 



the matrix contains fossils of the Tessini Fauna, it would appear 

 that, during the period represented by this latter fauna, a ridge 

 of Lower Cambrian sandstones, from which the superincumbent 

 Lower Cambrian limestones had been previously removed, was 

 exposed to denudation, and that it was broken down, with little 

 or no transportation of material, to form a sandy reef or shoal, 

 which quite locally became a basal deposit of the Middle Cambrian. 



(2) The fact that the Groomii Fauna of the Quarry-Ridge Grits 

 (also a basal deposit) is quite distinct from the fauna of the Breccia- 

 Bed, indicates that they are not contemporaueous, although both 

 belong to Middle Cambrian time. We have, therefore, within the 

 little district of Comley two basal deposits, separated in time by a 

 sufficient interval to allow of a definite change of faunas. 



(3) The exact horizon of the Groomii Fauna in the general 

 Cambrian succession cannot at present be stated definitely, but 

 that it is older than the fauna of the Breccia-Bed appears probable 

 from three considerations : — (i) The Conocoryphe which it contains 

 is allied to 0. emarginata Linnarsson, which is, so far as known, 

 confined to the (Elandicus Zone of Scandinavia. 



(ii) The fauna of the Breccia-Bed is more nearly related to the 

 Davidis Fauna of the Shoot-Itough-Eoad Beds of Comley than the 

 Groomii Fauna seems to be. 



(iii) The majority of the Lower Cambrian fossils found in the 

 included blocks of the basal conglomerate of the Quarry-Ridge 

 Grits belong to a somewhat higher horizon than those found in the 

 component blocks of the Breccia-Bed ; it may therefore be inferred 

 that more time was required for the denuding forces to reach the 

 parent rock of the latter, and the probability is that the Breccia- 

 Bed is the younger of the two basal deposits. 



VI. Conclusions. 



The lithological resemblance between the matrix of the Breccia- 

 Bed, yielding Paradoxides, and the beds of the Lower Cambrian 

 sandstone, yielding Olenellus (sensu lato), is so close that, were it 

 not for the presence of the fossils, it is doubtful whether I should 

 have recognized its true nature. It was fortunate that this exposure 

 was not discovered until after the local faunas of the Lower and 

 Middle Cambrian had been fairly well established ; for it is easy 

 to imagine how collections made from this spot near Comley Brook 

 might have been held to prove that Paradoocides and Olenellus 

 were, in part at least, contemporaneous, in which case the Breccia- 

 Bed would have been regarded as a passage-bed, where the two 

 faunas overlapped. 



In view of the fact that a reticulate surface to the test of tri- 

 lobites has hitherto, so far as known, only been found among 

 Lower Cambrian forms, special attention may be called to that 

 seen in Dorypyge retiadata, sp. nov. The resemblance to some 

 parts of the tests of Callavia from Comley is very close. 



This reticulation is characteristic of the genera into which 



