MIOCENE PLANTS AND INSECTS RELATED TO RECENT SPECIES.

Geologists were acquainted with about three hundred species of marine shells from the Falunian strata on the banks of the Loire, before they knew anything of the contemporary insects and plants. At length, as if to warn us against inferring from negative evidence the poverty of any ancient set of strata in organic remains proper to the land, a rich flora and entomological fauna was suddenly revealed to us characteristic of Central Europe during the Upper Miocene period. This result followed the determination of the true position of the Oeningen beds in Switzerland, and of certain formations of "Brown Coal" in Germany.

Professor Heer, who has described nearly five hundred species of fossil plants from Oeningen, besides many more from other Miocene localities in Switzerland,* estimates the phanerogamous species which must have flourished in Central Europe at that time at 3000, and the insects as having been more numerous in the same proportion as they now exceed the plants in all latitudes.

     (* Heer, "Flora tertiaria Helvetiae" 1859; and Gaudin's
     French translation, with additions, 1861.)

This European Miocene flora was remarkable for the preponderance of arborescent and shrubby evergreens, and comprised many generic types no longer associated together in any existing flora or geographical province. Some genera, for example, which are at present restricted to America, co-existed in Switzerland with forms now peculiar to Asia, and with others at present confined to Australia.

Professor Heer has not ventured to identify any of this vast assemblage of Miocene plants and insects with living species, so far at least as to assign to them the same specific names, but he presents us with a list of what he terms homologous forms, which are so like the living ones that he supposes the one to have been derived genealogically from the others. He hesitates indeed as to the manner of the transformation or the precise nature of the relationship, "whether the changes were brought about by some influence exerted continually for ages, or whether at some given moment the old types were struck with a new image."

Among the homologous plants alluded to are forty species, of which both the leaves and fruits are preserved, and thirty others, known at present by their leaves only. In the first list we find many American types, such as the tulip tree (Liriodendron), the deciduous cypress (Taxodium), the red maple and others, together with Japanese forms, such as a cinnamon, which is very abundant. And what is worthy of notice, some of these fossils so closely allied to living plants occur not only in the Upper, but even some few of them as far back in time as the Lower Miocene formations of Switzerland and Germany, which are probably as distant from the Upper Miocene or Oeningen beds as are the latter from our own era.

Some of the fossil plants to which Professor Heer has given new names have been regarded as Recent species by other eminent naturalists. Thus, one of the trees allied to the elm Unger had called Planera Richardi, a species which now flourishes in the Caucasus and Crete. Professor Heer had attempted to distinguish it from the living tree by the greater size of its fruit, but this character he confessed did not hold good, when he had an opportunity (1861) of comparing all the varieties of the living Planera Richardi which Dr. Hooker laid before him in the rich herbarium of Kew.

As to the "homologous insects" of the Upper Miocene period in Switzerland, we find among them, mingled with genera now wholly foreign to Europe, some very familiar forms, such as the common glowworm, Lampyris noctiluca, Linn., the dung-beetle, Geotrupes stercorarius, Linn., the ladybird, Coccinella septempunctata, Linn., the ear-wig, Forficula auricularia, Linn., some of our common dragon-flies, as Libellula depressa, Linn., the honey-bee, Apis mellifera, Linn., the cuckoo spittle insect, Aphrophora spumaria, Linn., and a long catalogue of others, to all of which Professor Heer had given new names, but which some entomologists may regard as mere varieties until some stronger reasons are adduced for coming to a contrary opinion.

Several of the insects above enumerated, like the common ladybird, are well known at present to have a very wide range over nearly the whole of the Old World, for example, without varying, and might therefore be expected to have been persistent throughout many successive changes of the earth's surface and climate. Yet we may fairly anticipate that even the most constant types will have undergone some modifications in passing from the Miocene to the Recent epoch, since in the former period the geography and climate of Europe, the height of the Alps, and the general fauna and flora were so different from what they now are. But the deviation may not exceed that which would generally be expressed by what is called a well-marked variety.

Before I pass on to another topic, it may be well to answer a question which may have occurred to the reader; how it happens that we remained so long ignorant of the vegetation and insects of the Upper Miocene period in Europe? The answer may be instructive to those who are in the habit of underrating the former richness of the organic world wherever they happen to have no evidence of its condition. A large part of the Upper Miocene insects and plants alluded to have been met with at Oeningen, near the Lake of Constance, in two or three spots embedded in thinly laminated marls, the entire thickness of which scarcely exceeds 3 or 4 feet, and in two quarries of very limited dimensions. The rare combination of causes which seems to have led to the faithful preservation of so many treasures of a perishable nature in so small an area, appear to have been the following: first, a river flowing into a lake; secondly, storms of wind, by which leaves and sometimes the boughs of trees were torn off and floated by the stream into the lake; thirdly, mephitic gases rising from the lake, by which insects flying over its surface were occasionally killed: and fourthly, a constant supply of carbonate of lime in solution from mineral springs, the calcareous matter when precipitated to the bottom mingling with fine mud and thus forming the fossiliferous marls.