| 1. Species continued unchanged | 28 | per cent. |
| 2. Species migrated from abroad | 7 | " |
| 3. Species continued with modification | 0 | " |
| 4. New species without known ancestors | 65 | " |
| 100 | per cent. |
He shows that the same or very similar proportions hold with respect to the cephalopods and trilobites, and, in fact, that the proportion of species in the successive Silurian faunæ which can be attributed to descent with modification is absolutely nil. He may well remark that in the face of such facts the origin of species is not explained by what he terms les élans poétiques de l'imagination.
The third part of Barrande's memoir, relating to the comparison of the Silurian brachiopods of Bohemia with those of other countries, though of great scientific interest, and important in extending the conclusions of his previous chapters, does not so nearly concern our present subject.
I have thought it well to direct attention to these memoirs of Barrande, because they form a specimen of conscientious work with the view of ascertaining if there is any basis in nature for the doctrine of spontaneous evolution of species, and, I am sorry to say, a striking contrast to the mixture of fact and fancy on this subject which too often passes current for science in England, America, and Germany. Barrande's studies are also well deserving the attention of our younger men of science, as they have before them, more especially in the widely-spread Palæozoic formations of America, an admirable field for similar work. In an appendix to his first chapter Barrande mentions that the three men who in their respective countries are the highest authorities on Palæozoic brachiopods, Hall, Davidson, and De Koninck, agree with him in the main in his conclusions, and he refers to an able memoir by D'Archiac in the same sense, on the cretaceous brachiopods.
It should be especially satisfactory to those naturalists who, like the writer, had failed to see in the palæontological record any good evidence for the production of species by those simple and ready methods in vogue with most evolutionists, to note the extension of actual facts with respect to the geological dates and precise conditions of the introduction of new forms, and to find that these are more and more tending to prove the existence of highly complex creative laws in connection with the great plan of the Creator as carried out in geological time. These new facts should also warn the ordinary reader of the danger of receiving without due caution those general and often boastful assertions respecting these great and intricate questions made by persons not acquainted with their actual difficulty, or by enthusiastic speculators disposed to overlook everything not in accordance with their preconceived ideas.
It may be asked, Is there, then, no place in the geological record even for theistic evolution? This it would be rash to affirm. We can only say that up to this time there is no proof of it. If nature has followed this method, she seems carefully to have concealed the process. If such changes have occurred as to evolve from a species, say of mollusk or coral, belonging to one geological period some form found in another period, and recognized as a distinct species, we have to suppose that the capacity for such change was in some way implanted in the species on its creation, and ready to be developed under favorable conditions or in the lapse of time. For example, we may suppose that a plant originating in the long arctic summers of a warm period might, on migrating southward into the alternations of day and night, undergo material changes. A marine animal long confined to a limited sea-basin might, on being permitted to expand over a wide submerged continent, be greatly modified in its structure and habits. Up to a certain point we know that such changes have occurred, and Barrande himself has largely illustrated them. As an example which I have myself studied, I may refer to the common shells known on our coasts as sand-clams (Mya truncata and Mya arenaria). The former species, in the cold waters of the Glacial Age, assumed a short form which it still retains in the arctic regions, and occasionally in the colder waters of the more temperate regions, though there a more elongated form prevails. Evidently the two forms are interchangeable according to the temperature of the water. Still, if we could imagine a permanent refrigeration over all the area occupied by the animal, the short form only might survive, and might be supposed to be a distinct species. This did not occur, however, even in the Glacial Age, and is not likely to occur. Further, the allied, though quite distinct, species Mya arenaria has lived with the other through all the long duration of the Post-Pliocene and modern periods, and, though having its own range of varietal forms, has preserved its distinctness. Cases of this kind are obviously of the nature of varietal, not specific, change.
In conclusion, the whole of the facts and laws above detailed point to a predetermined plan and to an intelligent Creator, of whose laws and modes of procedure we may learn much by patient and careful study. This surely gives a great additional interest to that marvellous story of the earth which in these last days has been revealed to us by the study of the rocks. We may also infer that not one method only but many have been employed in replenishing the earth at first with living beings, and in adding to these from time to time. To what extent we may be able to understand these, time and future discoveries will show. In the mean time, we can only suggest such general theories as those referred to in the first of these lectures, but can affirm that Agnostic Evolution is altogether abortive in its attempts to solve the problem of the chain of life in geological time.