March 16, 18 76 J 



NATURE 



389 



To begin with fishes : we will take as our first example 

 the very beautiful genus Beryx, a fish not unlike our sea- 

 bream, found widely distributed through the deep seas, and 

 extending to about 40'' on each side of the equator. Like 

 the perch or the sea-bream, it is a %xzz.\Xy spedalised ^^ ; 

 the head is immensely large, the bony rays supporting the 

 fins hard and unjointed, the ventral fins or represen- 

 tatives of the hind limbs situated just behind the head, 

 under the throat, the operculum curiously ornamented, and 

 the air-bladder completely shut off from the gullet ; thus 

 differing very markedly from a more generalised fish such 

 as the herring or carp, in which the head is proportion- 

 ally much smaller, the fin- rays soft and jointed, the 

 ventral fins far back, the operculum not ornamented, and 

 the air-bladder communicating by a duct with ^the oeso- 

 phagus. 



We now know that at depths greater than five or six 

 hundred fathoms, the sea-bottom is to a great extent com- 

 posed of a very fine greyish-white mud, sticky when first 

 removed from the water, but afterwards hardening into a 

 delicate friable stone, not at all unlike chalk. This mud, 

 which is largely made up of shells of the minute marine 

 organism Globigerina, forms the bed of thousands of 

 square miles of sea in which Beryx lives, and there can 

 be no doubt that when the fish dies it sinks to the bottom, 

 and, its soft parts being destroyed, becomes gradually 

 imbedded in the soft mud, there to remain until the present 

 sea-bottom is upheaved and becomes dry land. 



Now, as a matter of archaeological evidence, what is 

 known of the history of Berjx and of the source whence 

 it proceeded? Naturally it is useless to seek for such 

 evidence except in deposits formed under like conditions to 

 those in which the fish lives at the present day. Through 

 the whole of the Phocene and Miocene epochs no deep-sea 

 formations are known, but in the middle of the Eocene 

 period— a time so remote that tropical plants flourished 

 on the banks of the Thames, and crocodiles abounded in 

 this country — we are acquainted with an extensive deep- 

 sea deposit, the Nummulitic Umestone, which, besides the 

 fossU giving it its name, contains large quantities of 

 Globigerina, in all essential respects like that of the pre- 

 sent day. In this formation are found two forms closely 

 allied to Beryx, but with such slight differences as to 

 receive diiferent generic names ; these are known as 

 Acanus and Pristigaster. On passing from the Eocene 

 or lowest tertiary to the chalk or uppermost secondary 

 formation, which bears the closest possible resemblance 

 to the modern Atlantic mud— the two may, in fact, be 

 looked upon as belonging to one continuous series of 

 deposits — we find an actual Beryx, a fish differing 

 no more from the modem Berices than the various 

 modern species of Ber>x do from one another. 

 This fossil, owing to the fineness of the chalk-forming 

 mud in which it was buried, is so perfectly preserved, 

 that all the details of structure of its hard parts, even to 

 the ornamentation of the scales, can be compared with 

 those in the recent fish ; and in this way the niost con- 

 clusive evidence is obtained that the differences which 

 separate it from its modem relatives are of no greater 

 importance than those by which the recent species of 

 Ber>^x are distinguished from one another. 



Thus we have positive evidence that a fish altogether 

 like the Beryx of the present day, existed millions of years 

 ago, before the Alps, the Himalayas, or the Rocky Moun- 

 tains were upheaved, and has continued to live ever since. 

 In face of these facts we cannot but conclude that the 

 modem Ber>'x is derived from that of the chalk, and that 

 the hypotheses of its creation out of nothing, and of its 

 origin from inorganic matter are, for scientific purposes, 

 simply non-existant, 



As to the form from which the Ber>'x of the chalk was 

 derived, we have absolutely no evidence, for there is no 

 trace of any such fish in any lower formation. 



We now pass on to a fiish of a far older and less 



specialised type than Ber}'x — the genus Ceratodus, re- 

 cently discovered in Australia. This animal, which 

 attains a length of six feet, is distinguished by the pos- 

 session of very curious fins, consisting of a central lobe, 

 with a surrounding fringe of fin-rays, and by the character 

 of its teeth, which are produced into curious horn-like 

 processes, so arranged that those of opposite jaws interlock. 

 Ceratodus is probably a vegetable feeder, lives in fresh or 

 brackish water, and is said sometimes to leave its native 

 element and crawl about among the weeds on the bank. 

 It is enabled to do this by the fact that it can breathe air 

 directly as well as air dissolved in water ; it has, in fact, 

 besides gills, an organ which is altogether a half-way 

 house between the air-bladder of a fish and the lung of 

 an amphibian. 



In the Wealden, the most recent estuarine deposit of which 

 we have any knowledge, there is no trace of Ceratodus to 

 be found, but this is hardly surprising, as only two or three 

 smaU patches of the earth's surface formed at this epoch 

 have been examined, and animals have a geographical 

 distribution at all times. But on passing back to the 

 Trias, a formation as far from the chalk in point of time 

 as the chalk from the present day, we find teeth belonging 

 to an undoubted Ceratodus, in shape and in microscopic 

 structure, exactly like those of the modem Australian fish. 

 No other remains of the Triassic Ceratodus have as yet 

 been found, but teeth are known to be so important a 

 diagnostic character that no naturalist would have any 

 hesitation in naming the genus to which the fish bearing 

 such teeth should be assigned. 



Thus we have a far more astonishing eximple of a per- 

 sistent type than was afforded by our Ber>'x, and as in the 

 case of the latter fish, all trace of the actual genus Cera- 

 todus is lost at this point, and we are obliged to content 

 ourselves with a few singvilar hints as to the way in which 

 the type has come about. The most valuable of these 

 hints are obtained by a study of a singular group of fish 

 found in great abundance in the Old Red Sandstone. 

 These are distinguished by the possession of curious 

 fringed fins, unhke those of any other fish except Lepido- 

 siren and Ceratodus — in fact, one genus, Dipterus, has 

 fins quite like those of Ceratodus, and its teeth and skele- 

 ton were formed on just the same type. It is doubtful 

 whether there is any relation between Ceratodus and 

 Dipterus in the way of ancestry, but the resemblance 

 between them is remarkable. 



It must seem rather strange for a known evolutionist 

 to select as examples two fish like Beryx and Ceratodus, 

 which, of all others, seem most likely to support the notion 

 that species are immutable. The adverse side only of the 

 question has been stated to-night, the other side will be 

 treated of on future occasions. 



THE OLD RED SANDSTONE 



AT a meeting of the Glasgow Geological Society on 

 the 24th ult., Sir William Thomson, F.R.S., presi- 

 dent, in the chair. Prof Geikie, F.R.S., communicated the 

 results of recent researches into the " History of the De- 

 posits known as the Old Red Sandstoae." After a pre- 

 liminar>- outUne of our present knowledge on the subject, 

 he proceeded to consider the development of the Old Red 

 Sandstone in the British Isles under its accepted three- 

 fold division into Lower, Middle, and Upper. The Lower 

 member, wherever its true base can be seen, is found to 

 pass down conformably into the Upper Silurian rocks. 

 But a well-marked line of demarcation, both by physical 

 characters and fossil evidence, runs between the two 

 systems. The Silurian formations continue replete with 

 organic remains up to their uppermost zone ; but on 

 entering the red strata of the overlying system we meet 

 with a remarkably abrupt change, lor the fossils almost 

 wholly disappear, and those which occur belong for the 



