"We can account for the absence of ice-action and scratches,"said Cortlandt,"in one of two ways.Either the proximity of the internal heat to the surface prevents water from freezing in all latitudes,or Jupiter's axis has always been very nearly perpendicular to its orbit,and consequently the thermometer has never been much below thirty-two degrees Fahrenheit;for,at the considerable distance we are now from the sun,it is easy to conceive that,with the axis much inclined,there might be cold weather,during the Northern hemisphere's winter,that would last for about six of our years,even as near the equator as this.
The substantiation of an ice-cap at the pole will disprove the first hypothesis;for what we took for ice before alighting may have been but banks of cloud,since,having been in the plane of the planet's equator at the time,we had naturally but a very oblique view of the poles;while the absence of glacial scratches shows,I take it,that though the axis may have been a good deal more inclined than at present,it has not,at all events since Jupiter's Palaeozoic period,been as much so as that of Uranus or Venus.The land on Jupiter,corresponding to the Laurentian Hills on earth,must even here have appeared at so remote a period that the first surface it showed must long since have been worn away,and therefore any impressions it received have also been erased.
"Comparing this land with the photographs we took from space,Ishould say it is the eastern of the two crescent-shaped continents we found apparently facing each other.Their present form I take to be only the skeleton outline of what they will be at the next period of Jupiter's development.They will,Ipredict,become more like half moons than crescents,though the profile may be much indented by gulfs and bays,their superficial area being greatly increased,and the intervening ocean correspondingly narrowed.We know that North America had a very different shape during the Cretaceous or even the Middle Tertiary period from what it has now,and that the Gulf of Mexico extended up the valley of the Mississippi as far as the Ohio,by the presence of a great coral reef in the Ohio River near Cincinnati.
We know also that Florida and the Southeastern Atlantic States are a very recent addition to the continent,while the pampas of the Argentine Republic have,in a geological sense,but just been upheaved from the sea,by the fact that the rivers are all on the surface,not having had time to cut down their channels below the surrounding country.By similar reasoning,we know that the canon of the Colorado is a very old region,though the precipitateness of its banks is due to the absence of rain,for a local water-supply would cut back the banks,having most effect where they were steepest,since at those points it would move with the greatest speed.Thus the majestic canon owes its existence to two things:the length of time the river has been at work,and the fact that the water flowing through it comes from another region where,of course,there is rain,and that it is merely in transit,and so affects only the bed on which it moves.
Granting that this is the eastern of the two continents we observed,it evidently corresponds more in shape to the Eastern hemisphere on earth than to the New World,both of which are set facing one another,since both drain towards the Atlantic Ocean.
But the analogy here holds also,for the past outlines of the Eastern hemisphere differed radically from what they are now.
The Mediterranean Sea was formerly of far greater extent than we see it to-day,and covered nearly the whole of northern Africa and the old upheaved sea-bottom that we see in the Desert of Sahara.Much of this great desert,as we know,has a considerable elevation,though part of it is still below the level of the Mediterranean.
"Perhaps a more striking proof of this than are the remains of fishes and marine life that are found there,is the dearth of natural harbours and indentations in Africa's northern coast,while just opposite,in southern Europe,there are any number;which shows that not enough time has elapsed since Africa's upheaval for liquid or congealed water to produce them.Many of Europe's best harbours,and Boston's,in our country,have been dug out by slow ice-action in the oft-recurring Glacial periods.
The Black and Caspian Seas were larger than we now find them;while the Adriatic extended much farther into the continent,covering most of the country now in the valley of the Po.In Europe the land has,of course,risen also,but so slowly that the rivers have been able to keep their channels cut down;proof of their ability to perform which feat we see when an ancient river passes through a ridge of hills or mountains.The river had doubtless been there long before the mountains began to rise,but their elevation was so gradual that the rate of the river's cutting down equalled or exceeded their coming up;proof of which we have in the patent fact that the ancient river's course remains unchanged,and is at right angles to the mountain chain.
