64 



KNOWLEDGE. 



[April 1, 1891. 



that the young plant occupies only a small part of the 

 embryo-sac ; the rest is filled with nourishing material, 

 to absorb which a part of the stem of the embryo assumes 

 a shield-like shape — scutellum — and applies itself to it. 

 This is an (ilhuminmni seed ; but the shield is not developed 

 in all seeds of this kind. 



When a seed commences to germinate, water is absorbed, 

 and a great quantity of oxygen is taken in. The chemical 

 processes which go on, the limits of this paper will not allow 

 us to discuss. Let it suffice to say that the root passes 

 out by the micropyle, and fastens the plant firmly in the 

 soil. In the meantime, if the plant be albuminous, the 

 embryo is absorbing the nomishiug material by means of 

 its seed-leaves, and living on it ; while if exalbuminous, 

 as is that of the Bean, the food-material contained in the 

 cotyledons is gradually used up, so that these organs 

 soon lose their fleshy appearance. By this time the 

 plant has obtained a firm hold of the soil, and then the 

 seed-coat is thro-ftTi off, chlorophyll appears in the leaves, 

 and the young plant is enabled to start life on its own 

 account. 



NUMMULITES AND MOUNTAINS. 



By R. Lydekker. 



BOTH the proverb " as old as the hills," as well as 

 the phrase the " everlasting hills," are but the 

 expression of the natural tendency of the human 

 mind to regard all bills and mountains as the 

 most lasting and ancient objects with which we 

 are familiar. As, however, is so often the case, science 

 steps in and tells us that, although the proverb and the 

 phrase are true enough as regards human experience, yet 

 that when we go back and study the origin of things, as 

 revealed by geology, we find that many hills and moun^ 

 tains — and more especially the highest of them — are 

 actually among the very newest features in the physio- 

 gnomy of the earth, and that the expression " as old as 

 the plains " would, in many instances, be a far truer 

 simile than the one current. 



_ If, indeed, we reflect for a moment,, we shall be con- 

 vinced that the highest mountains of the globe — always 

 excepting volcanoes, which have the power of renewing 

 their height — must necessarily, as a general rule, be 

 yoimger than many of those of lower height, or even than 

 the plains from which they rise. Thus rain, snow, frost, 

 and rivers are perpetually tending to wear down and wash 

 away all the higher points of the earth's surface, and to 

 carry the dehris< to the valleys below. Consequently, we 

 are led to conclude that, i>rima fucie, the higher a moun- 

 tain range is, the less time it has been subject to this 

 vvashing-away process, and, therefore, the younger it is as 

 regards relative age. It might, indeed, be objected to this 

 that the mountains that are now the highest have always 

 been the highest ; and that at the beginning of all things 

 their original height as much exceeded their present height 

 as the latter does that of the smaller ranges. In this 

 \-iew, however, their original heights would have had to 

 be so stupendous as to be almost inconceivable, and 

 probably much greater than is compatible with the 

 physical conditions of the globe. This hypothesis may, 

 therefore, be dismissed as untenable ; more especially 

 as there is direct evidence of a totally different kind, 

 which is conclusive as to the truth o"f the alternative 

 view. 



This evidence is afforded by fossils, and more especially 

 by a particular kind of fossil, which, from its abundance 



and the restricted geological epoch in which it is found, is 

 of more than usual value in inquiries of the present 

 nature. 



If any of our readers have ever examined the Tertiary 

 clays and sands of Barton, in Hampshire, or of Bruckle- 

 sham, on the Sussex coast, they will probably have met 

 with numerous disc-like objects, the larger of which are 

 somewhat more than an inch in diameter, while the 

 smallest are scarcely bigger than a pin's head. When 

 split or cut, these objects are found to contain a number of 

 minute chambers, separated from one another by thin 

 walls arranged in the form of a spiral, as shown in the 

 figure. Technically they are known as nummulites, and 

 belong to the very lowest division of the animal kingdom 

 — lower even than the sponges, wliich some people cannot 

 be persuaded to believe are animals at all. Now these 

 nummulites are exceedingly interesting to those who study 

 the growth and formation of mountain ranges, for the 

 reason that they occur, in any quantity and of large size, 

 only through the greater portion of the Eocene or lowest 

 division of the Tertiary (latest) geological period, although 

 not reaching down to the London Clay ; and also because 

 they were very widely distributed in the seas which then 

 covered a large part of our existing continents. If, then, 

 we should find rocks containing great numbers of large 

 nummulites on the flanks or tops of a mountain range, we 

 should be assured that such range was younger than the 

 Eocene period, at which date its component rocks were 

 being formed as mud at the bottom of the sea. 



Now, although in England the aforesaid nummulites 

 only occur in soft beds of clay and sand in the low clifis of 

 the southern coast, when we cross to the Continent we 

 find them forming the greater part of a massive limestone, 

 known as the Nummulitic Limestone. This very charac- 

 teristic rock is more massive and more widely spread than 

 any other Tertiary deposit, and, in its thickness and 



A XcMMUI.ITE, VIKWKD FROM AnOVE. ANI> HoIil/.dXTALI.Y 



Bisected. 



identity of structure over large areas, recalls the Mountain 

 Limestone of the Palaeozoic epoch. It is, indeed, abso- 

 lutely one mass of nummulites, of which sections are 

 displayed on every fractured surface ; and it was probably 

 an open sea deposit, which must have taken incalculable 

 ages for its formation. It occurs in Southern Europe in 

 both the Alps and Pyrenees, attaining a thickness of 

 several thousand feet in the former, and occurring at 

 elevations of more than 10,000 feet above the sea-level. 

 In the Pyrenees it forms a beautiful white crystalline 

 marble. On the south of the Mediterranean, Nummulitic 

 Limestone is found again in the mountains of Algeria 

 and Morocco, in Eastern Europe it reappears in the 

 Carpathians, and thence may be traced into the Caucasus 

 and Asia Minor. All travellers to India are familiar with 

 the Mokattam range of bare mountains on the western 

 shore of the upper part of the Eed Sea, which are likewise 

 almost entirely composed of this same limestone. It is, 

 indeed, a common belief among the Egyptian peasantry 



