Aiigtcsl 26, 1880] 



NATURE 



403 



up of fragments from the surrounding gneiss. The 

 stones in this deposit are for the most part perfectly 

 angular, and are sometimes stuck on end in the mass. 

 They underwent but little re-arrangement after they were 

 thrown down, though occasional lenticular seams of red 

 sandstone running through the rock serve to prove that it 

 is lying as a flat cake on the gneiss. My friend Mr. 

 Norman Lockyer accompanied me in the examination of 

 this hill. We searched long for a striated stone among 

 the component materials of the breccia, but the matrix 

 was too firm to allow us to bare and extract any of the 

 pebbles or boulders. We traced, however, the characteristic 

 rounded bossy surface of the gneiss until it passed under 

 the breccia, and were convinced that, could the outlier of 

 breccia be stripped off, the same kind of surface would be 

 found below it as on the gneiss above and around. The 

 valley in which this little fragment of a once more exten- 

 sive deposit of breccia lies certainly existed as a hollow in 



Cambrian times. From the narrowness of its present 

 outlet, which has been cut by the escaping streamlet, and 

 from the nature of the breccia, we may infer with some 

 plausibility that the hollow was filled with water, and may 

 have been a lake. It was almost certainly a rock-basin, 

 surrounded with hills of gneiss that had been worn into 

 undulating dome-shaped hummocks. 



Behind the new hotel at Gairloch the ground rises 

 steeply into a rocky declivity of the old gneiss. Along 

 the base of these slopes the gneiss (which is here a 

 greenish schist) is wrapped round with a breccia of re- 

 markable coarseness and toughness. We noticed some 

 blocks in it fully five feet long. It is entirely made up of 

 angular fragments of the schist underneath, to which it 

 adheres with great tenacity. Here again rounded and 

 smoothed domes of the older rock can be traced passing 

 under the breccia, as at a in Fig. 4. On the coast imme- 

 diately to the south of the new Free Church a series of 



FlG.«4. — Sections of the ju 



f the fundamental gneiss and overlying Cambrian breccia. Gairloch. 



instructive sections again lays bare the worn undulating 

 platform of gneiss, with its overlying cover of coarse 

 angular breccia {/> in Fig. 4). 



On these far northern shores, then, there still remain 

 fragments of the surface on which our oldest sedimentary 

 accumulations were deposited. These fragments are 

 found to bear in their smoothed hummocky contours a 

 striking resemblance to the surface which geologists now 

 always associate with the action of glacier-ice. There 

 can at least be no doubt that they are denuded surfaces. 

 The edges of the vertical and twisted beds of gneiss and 

 schist have been smoothly bevelled off. These rocks, 

 however, would never have assumed such a contour if 

 exposed merely to ordinary sub-aerial disintegration. 

 They would have taken sharp craggy outlines like those 

 which are here and there gradually replacing the ice-worn 

 curves of the rochcs motdoniices. They ha\-e certainly 

 been ground by an agent that has produced results 

 which, if they were found in a recent formation, would, 



without hesitation, be ascribed to land-ice. The breccia, 

 too, is quite comparable to moraine-stuff. Without 

 wishing at present to prejudge a question on which I 

 hope yet to obtain further evidence, I think we have in 

 the meantime grounds for concluding that in the north- 

 west of Scotland there is still traceable a fragment of the 

 earliest known land-surface of Europe, that this primeval 

 country had a smooth undulating aspect not unhke that 

 of the west of Sutherland at the present time, that it 

 contained rock-hollows, some of them filled with water, 

 that into these hollows piles of coarse angular detritus 

 were thrust, that around and beneath the tracks where 

 this detritus accumulated the gneiss was worn into dome- 

 shaped forms strongly suggestive of the operation of 

 land-ice, and that though the ice of the last Glacial Period 

 undoubtedly ground down the platform of gneiss, bared 

 as it was of the overlying formations, it found a surface 

 already worn into approximately the same forms as those 

 which it presents to-day. Arch. Geikie 



EXCRETION OF WATER BY LEAVES^ 



TN the pamphlet referred to below Dr. Moll gives a detailed 

 ■*■ account of his investigations upon the excretion of drops of 

 water by leaves, of which an outline was given in the Botanische 

 Zeitung for January 23 of the present year. 



The question with which he more especially deals is as to 

 whether this excretion is a function which is performed by all 

 leaves, or whether it is confined to such leaves only as possess 

 specially modified organs. The method which he employed in 

 his researches is to place the leaves under the most favourable 

 condition for the excretion of drops by diminishing as far as 

 possible their transpiration, and by supplying them with water. 

 Under ordinary circumstances the excretion of drops is due to 

 the acrion of the root-pressure ; but Dr. Moll substitutes for this, 

 in his experiments, the pressure of a column of mercury, in order 

 to have this important factor in the problem completely under 

 control. 



The results, which are of considerable interest, may be briefly 

 stated as follows : out of sixty plants experimented on, the 

 leaves of twenty-nine excreted drops without becoming injected, 

 that is, without their intercellular spaces becoming filled with 

 water; thirteen leaves became injected and excreted drops, and 

 eighteen became mjected but did not excrete at all. It appears 

 that tlie age of the leaf has a very evident influence upon the 

 excretion of drops, for whereas the young leaves of a plant, such 

 as Sambuats niip-a or Plalaniis occidentalh, for instance, readily 

 excrete drops without becoming injected, the older leaves of the 



' '■ Untersuchungen uberTropfenausscheiiungur.d Injection bei Clattern," 

 von Dr. J. W. Mcll. (Amsterdam, iS8o.) 



same plant become injected and excrete scarcely at all. Under 

 these circumstances it is quite possible and even probable, a? Dr. 

 Moll himself suggests, that of the eighteen [ lants the leaves of 

 which became only injected, some at least were capable of 

 excretion at an earlier period. It is only definitely stated of 

 Hedera, Syriuga, and Taxus that their leaves do not excrete 

 at all. 



As to the organs of excretion, it is effected in eight out of the 

 forty two cases by means of water-pores, but in four of these 

 cases it is effected al.^o by ordinary stomata ; in eight other cases 

 it was found to be effected by stomata, and in three cases it took 

 place at portions of the siu-face which possessed neither water- 

 pores nor stomata. These last cases are carefully distinguished 

 by Dr. Moll from those in which an excretion took place over 

 the whole ^uiface of the leaf in consequence of exces ive 

 pressure. 



From these observations it appears that most leaves, at least 

 so long as they are comparatively young, are capable of excreting 

 water in drops when it is supplied to them in excess, and further, 

 that this excretion is effected by certain organs {Einissarien the 

 author calls ihem) which may be water-pores, or ordinary 

 stomata, or limited areas of the surface which are histologically 

 undifferentiated. The effect of this excretion is to prevent the 

 injection of the leaves when the root-pressure is great, a con- 

 dition which would obviously interfere with the circulation of air 

 in the intercellular spaces, and therefore with the function of the 

 leaf. Dr. Moll suggests that possibly some definite correlation 

 exists between the presence of excretory organs and the existence 

 of root-pressure in a plant; for instance, according to Hofmeisler 

 ("Flora," 1S62), no root-pressure can be detected in Conifers, 



