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Every geologist knows how full of interest and suggestiveness is this book of Darwin's on volcanic islands.
The relations of these different groups can not be learnt by the study of any one section; and the geologist who sets out with the expectation of finding a fixed order of succession may perhaps complain that the different parts of the basin give contradictory results.
Referring to this standard of magnitude, the geologist may admire the ample limits of his domain, and admit, at the same time, that not only the exterior of the planet, but the entire earth, is but an atom in the midst of the countless worlds surveyed by the astronomer.
At the upper end of the Cascades a boat awaits you, which carries you through yet more picturesque scenery to Dalles City, where you spend the night. This is a small place, remarkable to the traveler chiefly for the geological collection which every traveler ought to see, belonging to the Rev. Mr. Condon, a very intelligent and enthusiastic geologist, the Presbyterian minister of the place.
"I ask you one thing," he was saying. "Will it ever rain again?" "Certainly not," replied a geologist and a metaphysician together. "Rain being an agent of Time in the production of change, there can be no place for it under the present dispensation." "Then will not the crops be burned up? Will the fruits mature? Are they not withering already? What of wells and rivers, and the mighty sea itself?
The crushed and folded and dislocated strata are laid open to the weather as the horizontal strata, and as the upheaved masses of Archaean rock are not. Moreover, strata of unequal hardness are exposed, and this condition favors rapid erosion. In imagination the geologist is present at the birth of whole mountain-ranges. He sees them gestating in the womb of their mother, the sea.
"But," said Wilbur, turning excitedly to his uncle, as soon as the lecturer had closed, "isn't there anything that can be done to make those places what they were before?" "Not often, if it is allowed to go too far," said the geologist. "It takes time, of course, for all the soil to be washed away. But wherever the naked rock is exposed the case is hopeless.
James Croll, the Scottish geologist, in his Climate and Time, and latterly the old theory that ocean currents are due to the trade-winds has again come into favor. Indeed, very recently a model has been constructed, with the aid of which it is said to have been demonstrated that prevailing winds in the direction of the actual trade-winds would produce such a current as the Gulf Stream.
Where the sea now extends, land may at a former period have connected islands or possibly even continents together, and thus have allowed terrestrial productions to pass from one to the other. No geologist disputes that great mutations of level have occurred within the period of existing organisms.
The geologist sometimes finds in soft sandstones that the same action is repeated in a larger way where a thin fragment of hard rock has protected a column many feet in height against the rain work which has shorn down the surrounding rock. When water strikes the moistened surface it at once loses the droplike form which all fluids assume when they fall through the air.
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