Darwin, in his famous chapter on "The Imperfection of the Geological Record," has well shown how scanty and imperfect are the modern fossiliferous deposits. The progress of research has only confirmed and accentuated the argument there presented on this point. Thus Nordenskiold, the veteran Arctic explorer, remarks with amazement on the scarcity of recent organic remains in the Arctic regions, where such a profusion of animal life exists; while in spite of the great numbers of cats, dogs and other domestic animals which are constantly being thrown into rivers like the Hudson or the Thames, dredgings about their mouths have revealed the surprising fact that scarcely a trace of any of them is there to be found.[56]
Even the fishes themselves stand a very poor chance of being buried intact. As Dana[57] puts it:
"Vertebrate animals, as fishes, reptiles, etc., which fall to pieces when the animal portion is removed, require speedy burial after death, to escape destruction from this source (decomposition and chemical solution from air, rain-water, etc.), as well as from animals that would prey upon them."
If a vertebrate fish should die a natural death, which of itself must be a rare occurrence, the carcass would soon be devoured whole or bit by bit by other creatures near by. Possibly the lower jaw, or the teeth, spines, etc., in the case of sharks, or a bone or two of the skeleton, might be buried unbroken, but a whole vertebrate fish entombed in a modern deposit is surely a unique occurrence.
But every geologist knows that the remains of fishes are, in countless millions of cases, found in a marvelous state of preservation. They have been entombed in whole shoals, with the beds containing them miles in extent, and scattered over all the globe. Indeed, so accustomed have we grown to this state of affairs in the rocks we hammer up, that if we fail to find such well-preserved remains of vertebrate fishes, land animals, or plants, we feel disappointed, almost hurt; we think that nature has somehow slighted this particular set of beds. But where in our modern quiet earth will we go to find deposits now forming like the copper slate of the Mansfield district, the Jurassic shales of Solenhofen, the calcareous marls of Oeningen on Lake Constance, the black slates of Glarus, or the shales of Monte Bolca?—to mention some cases from the Continent of Europe more than usually famous in the literature for exquisitely preserved vertebrate fishes, to say nothing of other fossils. According to Dana, all these must have met with a "speedy burial after death"—perhaps before, who knows?
Buckland[58] in speaking of the fossil fish of Monte Bolca, which may be taken as typical of all the others, is quite positive that these fish must have "perished suddenly," by some tremendous catastrophe.
"The skeletons of these fish," he says, "lie parallel to the laminae of the strata of the calcareous slate; they are always entire, and so closely packed on one another that many individuals are often contained in a single block.... All these fish must have died suddenly on this fatal spot, and have been speedily buried in the calcareous sediment then in course of deposition. From the fact that certain individuals have even preserved traces of color upon their skin, we are certain that they were entombed before decomposition of their soft parts had taken place."
In many places in America as well as Europe, where these remains of fish are found, the shaley rock is so full of fish oil that it will burn almost like coal, while some have even thought that the peculiar deposits like Albertite "coal" and some cannel coals were formed from the distillation of the fish oil from the supersaturated rocks.
De La Beche[59] was also of the opinion that most of the fossils were buried suddenly and in an abnormal manner. "A very large proportion of them," he says, "must have been entombed uninjured, and many alive, or, if not alive, at least before decomposition ensued." In this he is speaking not of the fishes alone but of the fossiliferous deposits in general.
There is a series of strata found in all parts of the world which used to be called the "Old Red Sandstone," now known as the Devonian. In this, almost wherever we find it, the remains of whole shoals of fishes occur in such profusion and preservation that the "period" is often known as the "Age of Fishes." Dr. David Page, after enumerating nearly a dozen genera, says: