Notices of Memoirs — Rev. J. F. Blnhe — Sedimentary Deposits. 473 



The determination of the remains, claimed to be of a later Devonian 

 type, is equally unsatisfactory. The only Acanthodian sufficiently 

 well preserved for discussion is not specially related to the Devonian 

 forms, but has the elongate shape characteristic of the genera of the 

 Carboniferous and Permian periods. The Acanthodian fragment 

 compared with the Devonian Cheirolepis (which is not an 

 Acanthodian) is too imperfect for consideration. The so - called 

 scales of the Devonian Glyptolepis, or an allied genus, evidently 

 belong to the large Rhizodont already mentioned, and closely 

 resemble the scales of the Lower Carboniferous Rhizodiis itself. 

 The Australian fish, however, does not belong to the latter genus, 

 its teeth being round in transverse section. 



The most interesting of all the genera represented in the collection 

 is one rightly recognised by McCoy as an Elasmobranch allied to 

 the Carboniferous Gyracanthus. It is named Gyracanthides, and is 

 a round-bodied Acanthodian fish, appai'ently toothless, with the 

 comparatively small and spinous pelvic fins advanced far forwards, 

 as in Acanthodes. Its dorsal fins have not been observed, but its 

 small anal fin is armed with a spine. 



There is also evidence of a small Dipnoan fish with teeth and 

 scales like those of the Carboniferous and Permian Sagenodus. The 

 typically Carboniferous Palseoniscidse in the collection are related to 

 Monichihys. 



There is thus no abnormal mingling of genera in the Early 

 Palaeozoic fish fauna from the Broken River, Victoria. It is a typical 

 Carboniferous assemblage without any extraneous elements. 



V. — On the Original Form of Sedimentary Deposits. By Rev. 

 Professor J. F. Blake, M.A., F.G.S.' 



IN determining the position and outline of ancient continents by 

 observing the direction in which the sediment derived from 

 them thickens or thins, and in interpreting the significance of the 

 contours of the sea-bottom, it is necessary to consider what will 

 be the actual shape as a whole of any sedimentary deposit of single 

 origin in relation to the land whence it is derived. 



It has been assumed by several authors, both of text-books and 

 of special memoirs, that sedimentary deposits are thickest near their 

 source of origin, and that limestones are deposited at great distances 

 from the shore. The author gives reasons for taking a somewhat 

 different view. The action of tides and currents is considered as 

 a subsequent operation, the original form of the deposit is that 

 which would result in a tideless sea, in the case of a river carrying 

 detritus directly outwards. The coarse material, which is pushed 

 along the bottom of a river, fills up the angle between the lowest 

 level the river reaches and the constantly deepening bottom of the 

 sea, and the deposit is consequently wedge-shape towards the land 

 and sharply sloping seawards, like the tip of a railway embankment. 

 The detritus which floats consists of all that has too low a power 



1 Abstract of a paper read before the British Association, Belfast, Sept., 1902, in 

 Section C (Geology). 



