and twenty and three hundred and thirty as it had between ninety and one hundred.

This reduces the computation of the age of an oak to little more than guess-work. The Cowthorpe oak, the largest existing in England, reached at one time seventy-eight feet in circumference. Damory's oak, in Dorsetshire, was only ten feet less when it was so decayed that it was cut up and sold for fire-wood in 1755; and the Boddington oak, in the vale of Gloucester, was fifty-four feet at the base when it was burned down in 1790. It is needless to mention other English oaks which are also claimants to a remote antiquity; but it is obvious, from the very variable rate of the growth of oaks, that size establishes no indisputable title, and that the Cowthorpe oak need not therefore be the oldest English oak because it is the largest recorded. From Loudon's statistics of oaks are extracted the following notices of trees, according to their age and girth :

This table not only shows the great variability of growth, but, if we take the three specimens of one hundred years old, gives us the high average of seventeen feet as that of only the first century. Taking, then, as usual, the third as the average growth, we should require rather more than eight centuries for an oak of fifty feet, which reduces to a very small number the oaks in England that can claim a thousand years.

When, therefore, Gilpin, in his "Forest Scenery," speaks of nine hundred years as of no great age for an oak, it must be said that very few oaks can be named which by measurement would sustain their title to that age. Tradition, which is always sentimental, leans naturally to the side of exaggerated longevity. William of Wainfleet gave directions for Magdalen College, Oxford, to be built near the great oak which fell suddenly in the year 1788, and out of which the president's chair was made, in memory of the tree. Gilpin assumes that for the tree to have been called great it must have been five hundred years old, and, therefore, perhaps standing in the time of King Alfred. But it is clear that it need not have been a century old to have fairly earned the title of great, and that, therefore, a period of six centuries may have covered its whole term of existence.

We are certainly apt to underrate the possible rate of growth where a tree meets with altogether favorable conditions. The silver fir was only introduced into England in the seventeenth century by

Sergeant Newdigate; and one tree of his planting was thirteen feet. round when Evelyn measured it eighty-one years afterward. A comparison of the statistics of growth, as above collected with reference to the oak, indicates with respect to most trees a more rapid rate than is commonly supposed. Let us test the claims of some of the oldest limes. The Swiss used often to commemorate a victory by planting a lime-tree, so that it may be true that the lime still in the square of Fribourg was planted on the day of their victory over Charles the Bold at Morat in 1476. A youth, they say, bore it as a twig into the town, and arriving breathless and exhausted from the battle had only strength to utter the word "Victory!" before he fell down dead. But this tree was only thirteen feet nine inches in 1831, i. e., three hundred and fifty-five years afterward, and it would be extraordinary if a lime had not attained in that period greater bulk than even an oak might have reached in a century. The large lime at Neustadt, in Würtemberg, mentioned by Evelyn as having its boughs supported by columns of stone, was twenty-seven feet when he wrote (1664), and in 1837 it was fifty-four, so that within a period of one hundred and seventythree years it had gained as much as twenty-seven feet. Consequently, making allowance for diminished growth, we may fairly assume that two hundred years would have been more than enough for the attainment of the circumference of the first twenty-seven feet which it had reached in the time of Evelyn. No English lime appears to have reached such dimensions as would imply a growth of more than three centuries, though the lime at Depeham, near Norwich, which was forty-six feet when Sir Thomas Browne sent his account of it to Evelyn, sufficiently dispels the legend that all limes in this country have come from two plants brought over by Sir John Spelman, who introduced the manufacture of paper into England from Germany, and to whom Queen Elizabeth granted the manor of Portbridge.

It would be natural to expect the greatest longevity in indigenous trees, and, though it has been much disputed what kinds are native to the English soil, etymology alone would indicate that the following trees were of Roman importation: the elm (ulmus), the plane (platanus), the poplar (populus), the box (buxus), the chestnut (castanea). The yew, on the contrary, is probably indigenous, though its opponents find some reason for their skepticism in the fact that its larger specimens are chiefly found in church-yards and artificial plantations. In favor of its claim is the fact that its pretensions to longevity seem to be better founded than those of any other English tree, not even excluding the oak. A yew that was dug up from a bog in Queen's County was proved by its rings to have been five hundred and fortyfive years of age; yet for the last three hundred years of its life it had grown so slowly that near the circumference one hundred rings were traceable within an inch. Some great and sudden change for the worse

in the external conditions may have accounted for so slow a rate; but it would hardly be safe, with such evidence before us, to allow more than three feet a century as the normal growth of a yew, in which case the Fortingal yew in Scotland, fifty-six feet round in 1769, may have lived more than eighteen centuries; and a longevity in proportion must be accorded to the yews at Fountain's Abbey, or to the Tisbury yew in Dorsetshire, which boasts of thirty-seven feet in circumference. Hence tradition in this case would seem to contain nothing incredible when it asserts that the yews on Kingley Bottom, near Chichester, were on their present site when the sea-kings from the North landed on the coast of Sussex.

It is, however, but seldom that any real aid can be derived from tradition in estimating the longevity of trees. We have even to be on our guard against it, especially when it associates the general claim to antiquity by a specific name or event. In the classical period the tendency was as strong as it is still; and we should look to our own legends when tempted to smile at the Delian palm mentioned by Pliny as coeval with Apollo, or at the two oaks at Heraclea as planted by Hercules himself. Pausanias, traveling in Greece in the second century of our era, saw a plane-tree which was said to have been planted by Menelaus when collecting forces for the Trojan war, whence Gilpin gravely inferred that the tree must have been thirteen centuries old when Pausanias saw it. Tacitus calculated that a fig-tree was eight hundred and forty years old because tradition accounted it the tree whereunder the wolf nursed Romulus and Remus. Nor was Pliny's inference more satisfactory, that three hollies still standing in his day on the site of Tibur must have been older than Rome itself, inasmuch as Tibur was older than Rome, and they were the very trees on which Tiburtus, the founder of the former, saw the flight of birds. descend which decided him on the site of his city. There is of course no more reason to believe in the reality of Tiburtus than of Francion, the mythical forefather of France, or of Brute the Trojan, the reputed founder of the British Empire.

These things suffice to justify suspicion of trees associated with particular names, such as Wallace's Oak, or trees claiming to have been planted by St. Dominic or Thomas Aquinas. Our only safe guide is measurement, applied year by year to trees alike of known and of unknown age, of insignificant as of vast dimensions, and recorded in some central annual of botanical information, facilitating the work of comparison and the arrival at something like trustworthy averages. The experiment, moreover, has not been sufficiently tried whether our oldest trees are capable of an increased rate of growth by the application of fresh earth round their roots, favorable though the case of the Tortworth chestnut is to the probability of such a result. Until, therefore, such statistics are more numerous than at present, we must be content to rest in the uncertainty with regard to the ages of trees which the

preceding attempt to estimate them makes sufficiently manifest, and to arrive at no more definite conclusion than was long ago arrived at by Pliny, that "vita arborum quarundam immensa credi potest" ("The life of some trees may be believed to be prodigious ").-Longman's Magazine.

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SOME UNSOLVED PROBLEMS IN GEOLOGY.*

BY DR. J. W. DAWSON.

II.

GAIN: we are now prepared to say that the struggle for existence, however plausible as a theory, when put before us in connection with the productiveness of animals, and the few survivors of their multitudinous progeny, has not been the determining cause of the introduction of new species. The periods of rapid introduction of new forms of marine life were not periods of struggle, but of expansion-those periods in which the submergence of continents afforded new and large space for their extension and comfortable subsistence. In like manner it was continental emergence that afforded the opportunity for the introduction of land animals and plants. Further, in connection with this, it is now an established conclusion that the great aggressive faunas and floras of the continent have originated in the north, some of them within the Arctic Circle; and this in periods of exceptional warmth, when the perpetual summer sunshine of the Arctic regions co-existed with a warm temperature. The testimony of the rocks thus is, that not struggle, but expansion, furnished the requisite conditions for new forms of life, and that the periods of struggle were characterized by depauperation and extinction.

But we are sometimes told that organisms are merely mechanical, and that the discussions respecting their origin have no significance, any more than if they related to rocks or crystals, because they relate merely to the organism considered as a machine, and not to that which may be supposed to be more important, namely, the great determining power of mind and will. That this is a mere evasion, by which we really gain nothing, will appear from a characteristic extract of an article by an eminent biologist, in the new edition of the "Encyclopædia Britannica ”—a publication which, I am sorry to say, instead of its proper role as a repertory of facts, has become a strong partisan, stating extreme and unproved speculations as if they were conclusions of science. The statement referred to is as follows: "A mass of living protoplasm is simply a molecular machine of great complexity, the total results of the working of which, or its vital phenomena, * Address of the President of the American Association for the Advancement of Science, delivered at Minneapolis, August 15, 1883. Reprinted from "Science."

depend on the one hand on its construction, and, on the other, on the energy supplied to it; and to speak of vitality as anything but the name for a series of operations is as if one should talk of the horologity of a clock." It would, I think, scarcely be possible to put into the same number of words a greater amount of unscientific assumption and unproved statement than in this sentence. Is "living protoplasm" different in any way from dead protoplasm, and, if so, what causes the difference? What is a "machine"? Can we conceive of a self-produced or uncaused machine, or one not intended to work out some definite results? The results of the machine in question are said to be "vital phenomena"; certainly most wonderful results, and greater than those of any machine man has yet been able to construct! But why "vital"? If there is no such thing as life, surely they are merely physical results. Can mechanical causes produce other than physical effects? To Aristotle, life was "the cause of form in organisms." Is not this quite as likely to be true as the converse proposition? If the vital phenomena depend on the "construction" of the machine, and the "energy supplied to it," whence this construction, and whence this energy? The illustration of the clock does not help us to answer this question. The construction of the clock depends on its maker, and its energy is derived from the hand that winds it up. If we can think of a clock which no one has made and which no one winds a clock constructed by chance, set in harmony with the universe by chance, wound up periodically by chance-we shall then have an idea parallel to that of an organism living, yet without any vital energy or creative law; but in such a case we should certainly have to assume some antecedent cause, whether we call it "horologity" or by some other name. Perhaps the term "evolution" would serve as well as any other, were it not that common sense teaches that nothing can be spontaneously evolved out of that in which it did not previously exist.

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There is one other unsolved problem, in the study of life by the geologist, to which it is still necessary to advert. This is the inability of paleontology to fill up the gaps in the chain of being. In this respect, we are constantly taunted with the imperfection of the record; but facts show that this is much more complete than is generally supposed. Over long periods of time and many lines of being, we have a nearly continuous chain; and, if this does not show the tendency desired, the fault is as likely to be in the theory as in the record. On the other hand, the abrupt and simultaneous appearance of new types in many specific and generic forms, and over wide and separate areas at one and the same time, is too often repeated to be accidental. Hence paleontologists, in endeavoring to establish evolution, have been obliged to assume periods of exceptional activity in the introduction of species, alternating with others of stagnation-a doctrine differing very little from that of special creation as held by the older geologists.