242 



SCIENCE. 



[Vol. XXI. No. 535 



ring is very asymmetrical, being elongate in the major axis of 

 •the elliptical specimen. In Heterocentroiits, too (Figs. 3 and 5), 

 the body is elliptical and the ring is asymmetrical, being longer 

 in the direction of the major axis of the specimen. In this genus 

 (one figured from the Bermudas [5] and one from the Philippine 

 Islands [3]) there is only one ocular which borders the ring, a 

 second barely reaching it in 5 or not really doing so in 3, this is 

 not like the case presented in Fig. 8, the exceptional Strongy- 

 locentrotus, for there the lateral and not the median ocular is the 

 one which surely borders the ring. A number of undetermined 

 Echinoids at hand from the Pacific Ocean closely resemble 

 Strongylooentrotus, and in them the aboral ring is like Fig. 7. 



These comparisons have interesting morphological suggestions. 

 Dorocidaris is a central form, as well as an early one palseozoo- 

 logically, in it the oculars are neither wholly on nor wholly ex- 

 cluded from the ring; from it Diadema is a departure toward and 

 -Arbacia from the ring, and all three of these are tolerably radial 

 in symmetry. Hijjponoe is a slight departure from the regular 

 symmetry of the aboral ring, all the rest are not radial. The 

 elongations of Echinometra and Heteroc.entrotiis are in the same 

 plane. in each case, but the plane is not in the plane of the mad- 

 reporic plate, as it is in the departures from radial and toward 

 bilateral symmetry in clypeastrids and spatangids. The aboral 

 pole of Strongylooentrotus is very much out of radial symmetry, 

 though the shell in all other respects is very perfectly regularly 

 iradial. The meaning of the exceptional case presented in Fig. 8 

 might perhaps be understood as a reversion toward an ancestral 

 form in which the oculars wete all excluded from the aboral ring. 

 T cannot think of any adequate physiological explanation of the 

 relations of these bones in either Fig. 7 or Fig. 8. 



Hamline Biological Laboratory, March 34, 1893. 



THE CANALS OF MARS. 



ET S. E. PEAL, SIBSAGAB, ASAM. 



The question as to the distribution of land and water on the 

 planet Mars, and nature of the so-called ''canals," is one on 

 which there has of late been considerable speculation; and in 

 the hope of throwing some little light on the subject, it may not 

 be amiss to draw attention to a recent geological discovery relat- 

 ing to the distribution of land and w.ater on our earth. 



At no very distant period it was generally supposed that terres- 

 trial continents and oceans had frequently — or at least occasion- 

 ally — changed places, that oceanic islands, as a rule, were the 

 ■summits of submerged or emerging ranges, the last relics, or 

 forerunners, of extensive land masses. All this is now changed, 

 «.nd one of the most recent and important discoveries of modern 

 geology is the fact that the great continental masses and deep 

 •ocean floors are permanent features of the earth's crust. 



On p. 150, "Island Life," Mr. A. R. Wallace tells us that 

 -" there is the strongest cumulative evidence, almost amounting 

 to demonstration, that for all known geological periods our con- 

 tinents and oceans have occupied the same general position they 

 do now." And at p. 330, " during the whole period of geologic 

 itime, as indicated by the fossiliferous rocks, our continents and 

 ■oceans have, speaking broadly, been permanent features of our 

 ■earth's surface." Referring to ocean floors, Mr. J. Murray again 

 ■says, " The results of many lines of investigation seem to show 

 that in the abysmal regions we have the most permanent areas of 

 the earth's surface." While M. Faye points out that " under the 

 ■oceans the globe cools down more rapidly and to a greater depth 

 than beneath the surface of the continents. At a depth of 4,000 

 imetres the ocean will still have a temperature not remote from 

 •0° C. , while at a similar depth beneath the earth's crust the 

 ■temperature would be not far from 150° C." 



Last, Professor James Geikie, in his address to Section E, 

 geography, of the British Association, sajs, "We must admit 

 that the solid crust of the globe has always been, subject to dis- 

 tortion, and this being so, we cannot doubt that the general 

 trends of the world's coast-linas must have been modified from 

 •time to time by movements of the lithosphere. ... It seems to 



be the general opinion that the configuration of the lithosphere 

 is due to the sinking in and crumpling up of the crust on the cool- 

 ingand contracting nucleus." "According to Professor Winchell 

 the trends (of the great world ridges and troughs) may have been 

 the result of primitive tidal action. He was of opinion that the 

 transmeridianal progress of the- tidal swell, in early incrustive 

 times, on our planet, would give the forming crust structural 

 characteristics and aptitudes trending north and south. The 

 earliest wrinkles to come into existence, therefore, would be 

 meridianal, or submeridianal, and such is certainly the preva- 

 lent direction of the most conspicuous earth features." "So far 

 as geological research has gone, there is reason to believe that 

 the elevated and depressed areas are of primeval antiquity — that 

 they antedate the very oldest of the sedimentary formations. 

 We may thus speak of the great world-ridges as regions of domi- 

 nant elevation and of the profound oceanic troughs, as areas of 

 more or less persistent depression." 



The great areas of elevation and of persistent subsidence are 

 very distinctly marked out on our earth by a meridianal-lobed 

 arrangement, caused, as Professor G. H. Darwin thinks, by tidal 

 rupture during early stages of crust formation. Thisgreat recent 

 discovery is, therefore, one of the greatest importance to all 

 seeking for the solution of the problem of the distribution of 

 land and water on Mars. 



Tested by our moon, and viewing the marea as "seas" now 

 in some way solidified, the foregoing conclusions are borne out in 

 the most remarkable manner on the hemisphere which is pre- 

 sented towards us. 



From Walter to Cassini we have distinct evidence (of different 

 kinds) of the existence along the prime meridian of avast shoal 

 or submerged continent lying north and south, bordered on the 

 east by the series of marea, Nubium,0. Procellarum, andlmbrium, 

 and on the west by Nectaris, Tranquilitatis, and Serenitatis, each 

 series of three marea having a meridianal trend. Near the limb 

 again, east and west, we see the well-known two series of vast 

 walled plains, lying north and south, the great Sirsalis cleft, also 

 north and south, 400 miles long, being a vast anticlinal surface- 

 fracture. 



That the persistent subsidence of ocean floors (an axiom in ter- 

 restrial geology) is also clearly seen in our moon, is well illus- 

 trated in tlie remarkable arrangement of the clefts in relation to 

 the marea, viewed as areas of subsidence. In regard to this 

 question, Mr. A. C. Ranyard in Knowledge, September, p. 173, 

 says: " The evidence brought forward by Air. Peal, with regard 

 to the general subsidence of the great lunar marea seems to me 

 conclusive." So that the two features of slow subsidence of 

 ocean floors and meridianal arrangement of the land and sea 

 areas due to primeval tidal rupture during crust formation, are 

 seen on both globes of the earth-moon system. 



But the arrangement of the land and sea areas on Mars is on a 

 totally different plan, there is an entire absence of equatorial 

 oceans, and of meridianally placed coiltinents divided, as in our 

 case and the moon, by wide troughs of subsidence. We see on 

 that globe two vast polar oceans divided by a more or less con- 

 tinuous land girdle. 



We may reasonably assume that on Mars the icrust-formation 

 began on the poles, and that, as time went on and further con- 

 densation took place, subsidence and formation of polar sea- 

 basins would ensue, their floors, being the coldest and densest 

 portion of the crust, persistently sinking in, would naturally 

 cause the emergence of the equatorial land-girdle. The compara- 

 tively unbroken continuity of this latter would again be due to 

 the absence of a large satellite causing tidal rupture: there 

 would be no breakingup of the emerging land girdle round 

 the equator, during crust-formation, as in the earth-moon 

 system. 



Professor G. H. Darwin thinks that the effect of solar tides on 

 Mars must be " inconsiderable," they might yet, however, be 

 sufficient to cause and maintain a slight overspill from one polar 

 ocean-basin into the other, as the northern or southern hemi- 

 spheres were presented towards the sun. 



During the equinoxes, also, for some months, twice a year, 

 solar attraction would probably draw the water from each polar 



