November i8, 1892,] 



SCIENCE. 



283 



of the earth relatively to the moon. And, according to that 

 theory [in the 6rst paper], in very early times the moon was very 

 near the earth, whilst the relative angular velocity was compara- 

 tively great. Now, this sort of motion, acting on a mass which 

 is perfectly homogeneous, would raise wrinkles on the surface 

 which would run in directions perpendicular to the axis of greatest 

 pressure. In the case of the earth, the wrinkles would run north 

 and south at the equator, and would bear away to the eastward 

 in northerly and southerly latitudes, so that at the north pole the 

 trend would be north-east, and at the south pole north-west. 

 Also the intensity of the wrinkling force varies as the square of 

 the cosine of the latitude, and is thus greatest at the equator and 

 zero at the poles. Any wrinkle, when once formed, would have 

 a tendency to turn slightly, so as to become more nearly east 

 and west than it was when first made. 



"The general configuration of the continents (the large wrin- 

 kles) on the earth's surface appears to me remarkable when viewed 

 in connection with these results. There can be little doubt that, 

 on the whole, the highest mountains are equatorial, and that the 

 general trend of the great continents is north and south in those 

 regions. The theoretical directions of coast-line are not so well 

 marked in parts removed from the equator. 



"The great line of coast running from north Africa by Spain 

 to Norway has a decidedly north-easterly bearing, and the long 

 Chinese coast exhibits a similar tendency. The same may be ob- 

 served in the line from Greenland down to the Gulf of Mexico; 

 but here we meet a very unfavorable case in Panama, Mexico, 

 and the long Californian coast-line. 



" From the paucity of land in the southern hemisphere, the 

 indications are not so good, nor are they very favorable to these 

 views. The great line of elevation which' runs from Borneo 

 through Queensland to New Zealand might perhaps be taken as 

 an example of a north-westerly trend. The Cordilleras run very 

 nearly north and south, but exhibit a clear north-westerly twist 

 in Tierra del Fuego, and there is another slight bend of the same 

 character in Bolivia." 



After speaking of his theory as in accordance with the views of 

 geologists, so far as they hold that the general position of conti- 

 nents is what it was from the first, Mr. Darwin remarks: 



" An inspection of Professor Schiaparelli's map of Mars (1878), 

 I think, will prove the north and south trend of continents is 

 something [not] peculiar to the earth. In the equatorial regions 

 we there observe a great many very large islands separated by 

 about twenty narrow channels running approximately north and 

 south. The northern hemisphere is not given beyond lati- 

 tude 40°, but the coast-lines of the southern hemisphere ex- 

 hibit a strongly marked north-westerly tendency. It must be 

 confessed, however, that the case of Mars is almost too favorable, 

 because we have to suppose, according to the theory, that its dis- 

 tortion is due to the sun, from which the planet must always 

 have been distant. The very short period of the inner satellite 

 shows, however, that the Martian rotation must have been (ac- 

 cording to the theory) largely retarded; and where there has been 

 retardation, there must have been internal distortion." 



The later map {Popular Science Monthly, 1889) after Schiapa- 

 relli's observations in 1888, gives the Martian surface from 70° 

 north to 70° south. The number of lines, including those of so- 

 called islands and coasts, running north-easterly, are about equal 

 to those running north-westerly ; although, east of 280° longitude 

 the lines are most strikingly north-westerly for about half the 

 surface of the planet, as any one can observe, inverting the map 

 to bring the north to the top, and the west to the left hand (see 

 "Septentrio" and "Oocidens" printed in the border of the map). 

 Beginning with the west, the longest north-west lines (all 

 double) and their angles with the equator are as follows, indicated 

 by names connected with them: Oreus, 20°; Pyriphlegethon, 47° 

 to 50° (both continued on the east in the map) ; Hydractes-Phlege- 

 thon, 24°; and Antseus-Eunastos, 40°, with virtual long continua- 

 tions extending it from 40° south to 60° north. The mean in- 

 clination of these four is about 34° ; and a striking fact is that 

 two are 20-24", and two 40-45° nearly. The mean of ten most 

 noticeable north-west lines, double or single, is about 42° 44'. 

 The longest north-east lines, also double, are Gigas, the in- 



clination changing from 40° on the south of the equator to 30° 

 on the north; Phison. 45°; and Erebus-Cerberus, somewhat 

 curved, 25"; of great length, and continued as a single line east 

 through not less than 150° of longitude. The mean is about 43°, 

 excluding the double Jumana, 75°. Twelve conspicuous north- 

 east lines, single or double, have a mean inclination of nearly 

 50° 45'. A few others are north and south, or so nearly so as to 

 be counted such. 



For comparison, a map of the earth on Mercator's projeection 

 must be taken. The mean of ten of the most noticeable north- 

 western trends of coast, mountain, or depression is 60°, as against 

 42° 44' in Mars. The mean of fourteen north-east is about46° 25', 

 as against 50° 45' of the twelve above mentioned in Mars, — a 

 striking similarity. The great features, running north and south, 

 are few, as in Mars; viz., the southern Andes, the Ural Moun- 

 tains ; and the less-known chain of eastern Africa. 



Mr. G. H. Darwin's theory is, so far as known to the writer, the 

 best one for the earth, and the only one fairly worked out, 

 though, as Mr. Darwin acknowledged, it is poorly consistent with 

 the earth's great north-west lines, and is seemingly opposed to 

 the tidal probabilities of Mars, which has two small but near 

 moons of different revolution. It would be exceedingly interest- 

 ing if some mathematical astronomer would work out the com- 

 plicated problem of the tides of Mars (perhaps considerable at 

 conjunctions) on the supposition that its surface was all water. 

 But Mr. Darwin partly dismisses the moons, and refers to the ac- 

 tion of the sun, which, however, he thinks must have been incon- 

 siderable. This reference is curiously coincident with a reported 

 suggestion bj the late Professor Benjamin Peirce that our con- 

 tinental trends might be due to the "action of the sun." I cannot 

 get from his son, through a friend, any reference to a record of 

 his view; only that in a perhaps unpublished paper, or on some 

 occasion, he called attention, as everyone knows he did, to the 

 remarkable fact that the continental trends are great circles of 

 the sphere tangential to the arctic and antarctic circles, — a fact 

 with some striking illustrations, but not universal. Professor 

 Dana credits the first observation of this to Robert Owen, in his 

 " Key to the Geology of the Globe," 1857. 



Professor James D. Dana suggested that the great lines of the 

 earth might be due to a system of cleavage comparable to that of 

 crystals.' He refers to parallelism observed in the crystals of a 

 solidifying mass, but does not give particulars. In some crystal- 

 line rocks, e. g. , gneiss, the parallelism conforms to layers of de- 

 posit, and here and in other instances may also have to do with 

 pressure. How it is in respect to unstratified metamorphic rocka 

 is a question to be determined by observation. There is one fact 

 on a limited scale that may have some weight; it is that, in cavi- 

 ties and fissures, implanted crystals have been observed to have 

 uniform alignment to the horizon and points of compass, — similar 

 faces of like crystals flashing simultaneously in the light. The 

 importance of this fact, so far as it holds true, is that the arrange- 

 ment must depend on some other force than molecular attrac- 

 tions; it may be from a very far-reaching cause, sufficient to 

 produce lines of weakness, here and there, that became concur- 

 rent. Perhaps we shall have to fall back provisionally on that 

 fetish of the ignorant and the semi-scientific, "electricity," sup- 

 posed to explain everything from a tornado to a nervous twinge. 

 In this case it might have a color of possibility, if it be true that 

 1 " Cleavage Structure In tlie Earth's Crust.— The prevalent north-east and 

 north-west courses of trends, the curves In the lines varying the direction 

 from these courses, and the dependence of the outlines and feature-lines of 

 the continents and oceanic lands upon these courses (p. 29) are the profoundest 

 evidence of unity of development in the earth. Such lines of uplift are llnea 

 of fracture or lines of weakest cohesion; and, therefore, like the courses of 

 cleavage in crystals, they show hy their prevalence some traces of cleavage, 

 structure In the earth, — in other words, a tendency to break in two transverse 

 directions rather than others. 



" Such a cleavage-structure would follow from the mode of origin of the 

 earth's crust. The crust has thickened by cooling until now scores of miles 

 through; and very much as ice thickens — by additions to its lower surface. 

 Ice takes a columnar structure, perpendicular to the surface, in the process, 

 so as often to break Into columns on slow melting. The earth's crust contains 

 as its principal ingredient one or more kinds of feldspar, all cleavat)le min- 

 erals; and, as crystals on slow solidification often take a parallel position, so It 

 might have been in the cooling crust. This appears the more probable when 

 it is considered with what extreme slowness the thickening of the crust has 

 gone on, and the immeasurable length of time it has occupied.''— Dana's 

 " Manual of Geolrgy," 18V6, pp. 737-8. 



