414 



FARMERS' REGISTER. 



win gives tiie deptfie as being witiiin those num- 

 bers. The great circular coral wail, built by my- 

 riads of minute architects, ascends sheer and 

 steep on both sides. "Externally," says M r. Dar- 

 win, '• the reef rises Irom an ocean prolbuudly 

 deep. The structure is analogous to that of a la- 

 goon, but with an island standing, like a picture 

 in its frame, in the middle." 



Of the construction of these encircling reefs, 

 what explanation can be given 1 No one as far as 

 we are aware, has hitherto attempted it with any 

 thing iilie success. It is hardly to be supposed 

 that reef-building poZi/pi of every dilTerent genera 

 should act in concert. Why should the reef spring 

 up at the distance of miles from the shore, and 

 Irom a depth, whilst we know that reels — the in- 

 stances are innumerable — grow attached to the 

 shore 1 



JVlr. Darwin believes that this problem receives 

 a simple explanation, Irom the Ikct, thai while the 

 land slowly subsides from changes in progress in 

 the subterranean regions, the reels of living coral 

 continue to grow to the surface. The line of ar- 

 gument which seems to have led him to the con- 

 clusion we shall stale; but first let us remind those of 

 our readers who may be only partially acquainted 

 with the progress of recent geological inquiry, 

 that proofs of the rise of the land have come in 

 from all quaiters of the world, ll', then, the globe 

 be not absolutely swelling like the frog in the 

 fable, which no one will grant, there must be tracts 

 which have lately undergone subsidence, or are 

 undergoing it. In ancient times such movements 

 of subsidence have taken place, attested, as every 

 geologist knows, by the vertical trees in the Port- 

 land dirl-beds, the alterations of fresh-waler and 

 marine deposites, &e. &c. 



Mr. Darwin, then, having' these facts in his 

 mind, seems to have been led to consider how it 

 €omes that enormous areas of deep ocean (p. 558) 

 are studded with low coral islands, and yet that 

 many facts show that reef-buildinir poZy;)/' do not 

 flourish at greater depths than twenty taihonis at 

 most. NVliat foundation, then, have these coral 

 islands in spaces of many thousand square leagues 

 of a deep, deep ocean? Must we suppose that 

 there are as many submarine mountams as co- 

 ral islands, all rising within twenty fa'homs 

 of the surface of the ocean, and not one above 

 it? Such a supposition will he rejected as mon- 

 strous. The only possible alternative then, as it 

 seems to us, is, that " as each point, one after the 

 olher according to its altitude, was submerged, the 

 coral grew upwards, and lijrmed the many islets 

 now standing at one level." (p. 5.58.) 



JMr. Darwin next consiJeis whether the pecu- 

 liar structure of the lagoon islands and encircling 

 reelis occurring in these oceans, which he is 

 forced by the (i)regoing arirument to helieve have 

 subsided, receives any explanation (i'om this move- 

 ment. He says, in substance — let an island fring- 

 ed with coral reefs very gradually subside, will not 

 the necessary ed'ect of tliis l)e, that although the 

 reef may grow upwards and reach the sur/iicc, it 

 will not be so with the land, which will gradually 

 be submerged ? I'hen, accorditig to the amount 

 of subsidence so will the width of the chaniu'i he 

 between the reef and shore. If the sinking conti- 

 nue, the encircled island, l)y the gradual submer- 

 gence of the last and hiaiiesi peak, will becoiiver- 

 verted iu'o a Ingoon ishuid. Mc. Daruia then ob- 



serves (p. 689), that the non-filling up of the interior 

 basin ol'ihe lagoon, on the open channel within the 

 enciicling reef, is due to those stations being un- 

 fiivorable (partly ov, ins to the sand and mud drift- 

 ed about) !o the giowth of the massive corals. 

 He proceeds to state that a series can be shown 

 from an annular reelj encircing either one or seve- 

 ral small islands, to a lagoon island which merely 

 encircles a sheet of water ; and he insists that the 

 diflerence been the various kinds of reefs (p. 556) 

 entirely lies in the absence or presence ol' neigh- 

 boring land, and tb.e relative position which the 

 reels bear to it. Mr. Darwin, therelbre, supposes 

 that as a reef fringing an island is converted by 

 subsidence into an encircled one, so a reef (rimming 

 the shore of a continent will be converted into a bar- 

 rier reef (p. 559), like that extraordinary one 

 on the N. E. cost of Australia, separated from 

 the land by a wide arm of the sea ; and there the 

 reels (p. 564) supposed to be produced by the 

 same kind of movement are found m juxtaposition. 

 The reels of New Caledonia exhibit a step be- 

 tween an encircling and a barrier reef. 



Mr. Darwin seems to think that, if this theory 

 be, rejected, not only must the origin of lagoon 

 islands encirclmg a barrier of reefs, and their pre- 

 sence in one part and entire absence in another, 

 remain altogether without explanation — which, 

 considering their vast nua)ber and unilbrmity ol' 

 structure, would be not a little remarkable ; — but 

 that all the facts showing that reel-building /)oZy/j/ 

 will not live at great depths must be rejected ; i'or 

 we must then suppose that the ree.'-s have sprung 

 up from submarine mountains, which we cannot 

 grant, over spates of many thousand square 

 leagues. If, on the other hand, this theory, which 

 includes under one head the origin of the several 

 reels, he admitted, very in)poriant deductions nmst, 

 follow from it ; lor it shows that great portions 

 of the surface of the globe have recently (in a 

 geological sense) undergone movements of sub- 

 sidence (which It must always be extremely dif- 

 ficult to detect by any direct evidence); and what 

 is even more worthy of note, it shows that the 

 movemems have been so liir gradual, that no one 

 sirdiing down has carried the reel" below the small 

 depth from which the polypi could rear it to the 

 surliAce again. So far so good ; but Mr. Darwin 

 alludes to even more extended inferences, which 

 we shall not notice, as the subject will soon be 

 treated by him at full length. 



ON THE SUPKRIOR ADVANTAGES OP GROW- 

 ING ORCHARD GRASS WITH RED CLOVER. 



From tlie Germantown Telegraph. 



Read before tlie Pluladclpliia Society ("or promoting Aciiculttire, 

 March 4, 1640, l)y Jaiwes Mease, M. D., V. President. 



My attention was first called to this subject 

 when reading the late Mr. iiardley'e 'Notes on 

 Ilusfiandry,' (1799,) in which he stales the 

 benefits to be derived from the sowing together 

 the two grasses first mentioned, and his remarks 

 appeared so well Ibunded in reason, that I was 

 disposed to |)ursue the practice he recommended; 

 but before trying the experiment, I consulted the 

 late Algernon Roberts, of Pliiladelphia county, 

 one of our best firmers, on the subject, and was 

 pleased to hear him approve of the measure. 



