4TO 



NA TURE 



{March 8, 1877 



the inequality in tiie inclinatidn of the moon's orbit, and 

 in the motion of her nodes. He determined with new 

 accuracy the astronomical refractions from an altitude of 

 45° down to the horizon, where he found it to be 34' ; and 

 be made a vast collection of observations on the planets, 

 which formed the groundwork of Kepler's discoveries, and 

 the basis of the Rudolphine Tables." 



MINIATURE PHYSICAL GEOLOGY 



THERE have appeared from time to time in the 

 columns of Nature, interesting and instructive 

 letters on the subject of Miniature Physical Geology. 

 May I be allowed to continue this subject, by pointing 

 out a few lessons which may be learnt during spare half- 

 hours on Ramsgate Sands. 



Not far to the east of the harbour, there bubbles up a 

 little stream, which, when the tide is low, flows for a con- 

 siderable distance over the sands before it reaches the 

 sea. Small as it is, this offers an excellent miniature 

 example of a large river, and from it several things may 

 be learnt. In the first place the river, when carefully 

 watched, is seen repeatedly, and with more or less rapidity, 

 to change its course. This is effected by the deflection^ 

 from some cause or other, of the main course of the stream 

 against one bank ; the result of which is that the bank is 

 forced to recede, and, as it does so, it ceases to be a 

 shelving slope, and becomes a tiny cliff of greater or less 

 relative height. This bank continues to be rapidly under- 

 mined by the action of the stream, and the upper portions, 

 now and again, topple over, with a little splash, into the 

 water, in a manner with which those who have travelled 

 on the Mississippi are well acquainted. In this way a 

 bold curve is formed, which increases in length down- 

 stream. 



In the meanwhile, on the opposite shore of the river, 

 sand is deposited, and, as the river cuts its way down- 

 wards, this portion is left high and dry. 



But, ere long, the deep water channel shifts — often 

 rapidly, and without apparent cause — and the miniature 

 river tends to resume a straight course ; it recedes from 

 its bank cliffs, and soon a tract of comparatively level dry 

 land separates these banks from the stream. After ad- 

 vancing, however, for a while in this direction, until it 

 there forms a curve similar to the one described above, it 

 once tnore swings in the direction of its former course, 

 until, by a continuance of the same processes, a broad 

 valley is formed, with beautifully-marked river terraces 

 on either side, showing the length of swing of the river on 

 each occasion that it oscillates to and fro. 



In the midst of the stream sand islands are from time 

 to time formed, partly by the deepening of the main 

 channel on one side or the other ; but, no sooner has the 

 sand of which they are composed become dry, than the 

 treacherous stream ccmtnences the destruction of that 

 which itself had produced. 



This is exactly what is continually taking place in the 

 Delta areas of most great rivers. In the Para branch of 

 the Amazons a large island (Parraqueet Island) has, 

 within the last quairter of a centuly, cotnpletely disap- 

 peared. The Ihla Nova has arisen, and is now covered 

 with a luxuriant vegetation. 



During the repeated changes in the course of our 

 miniature river, it is possible to watch the deposition of 

 a layer of coarse sand on the partially-eroded surface of 

 a bed of finer material, and it is interesting and instruc- 

 tive to notice how great a body of the coarse material is 

 dragged along the bottom. Even in the most sluggish of 

 my mitiiatiire streams the sand-grains might be seen 

 rolling over afid over each other as they travelled sea- 

 wards. 



In the thore muddy flats of Pegwell Bay, I, on one 

 occasion, had an opportunity of witnessing the formation 



of that which is known on the Mississippi as a "cut-off." 

 The miniature stream bent round in a great loop, and as 

 the flow of the water caused the concave banks to recede, 

 the loop was gradually converted into a circle of water, 

 and, the main stream flowing through the shortest course, 

 left a " horse-shoe " lake, which was in time almost com- 

 pletely shut off from the miniature river. 



Perhaps one of the most interesting of these spare 

 half-hours may be spent in watching the formation of 

 deltas. Numbers of these miniature rivers flow into 

 pools, which are miniature seas or lakes. I have often 

 seen one of the streams in the course of an hour fill uo 

 a considerable bay, and push its delta far out to sea. The 

 grains of sand, when they come to rest in the pool, form 

 a slope of very constant angle, which, by a number of 

 measurements, I found to be 40° for coarse sand, and 

 34° for fine sand, the average angle being 36°. By watch- 

 ing the advance of the delta, the formation of false bed- 

 ding may be seen in actual progress. But these pools, 

 ot miniature seas, which lie in depressions in the chalk, 

 offer a field for the study of marine denudation. One 

 may see, for instance, the waves advancing over a newly- 

 formed delta, planing off the upper portion, and forminjj 

 tiny cliffs of delta material, but leaving the deepver parts 

 of the slope of the deposit intact. 



Again, during gentle and steady breezes one may see 

 the formation of drift-currents. I remember watching 

 with interest such a current, which flowed between tiny 

 chalk cliffs through the straits which separated two 

 miniature seas ; the most instructive point being that the 

 finer grains of sand at the bottom of the straits^ where 

 the water was some 7 inches deep, were rolling over each 

 other in such a manner as to prove the existence of an 

 under-current setting in the opposite direction to that in 

 which the surface-current was flowing. 



There are many other lessons which may be learnt — 

 such as the formation of fan-deposits (similar to those 

 so plentiful in the Rhone valley and elsewhere in Switzer- 

 land), which are formed at the foot of the miniature chalk 

 mountains, that stand out from the sand ; and the stop- 

 page of the sand ripples, or miniature sand dunes, by the 

 tiniest stream, reminding us of the way in which the 

 Nile has preserved Egypt from total obliteration by this 

 material ; but I have already occupied enough of your 

 space. 



My object in drawing attention to such matters of ordi- 

 nary observation is to induce students of physical geology 

 to go out and observe these things for themselves. If, 

 after a morning's study of Lyell's " Principles," the young 

 geologist will devote an hour's careful observation to 

 miniature physical geology, with sketch and note-book 

 in hand, he will find that his conceptions have a reality 

 and a solidity which could not have been evolved in the 

 study at home, while at the same time he will find it more 

 easy to follow, when he shall have the opportunity, the 

 workings of nature on a grander scale. 



C. Lloyd Morgan 



TESTIMONIAL TO MR. DARWIN— EVOLU- 

 TION IN THE NETHERLANDS 



WE have great pleasure in printing the following 

 correspondence : — 



To the Editor of Nature. 



Utrecht, February 20, 1877 

 On the sixty-eighth birthday of your great countryman, 

 Mr. Charles Darwin, an album with 217 photographs of 

 his admirers in the Netherlands, among whom are eighty- 

 one Doctors and twenty-one University Professors, was 

 presented to him. To the album was joined a letter, of 

 which you will find a copy here inclosed, with the answer 

 of Mr. Darwin. 



