Page:Popular Science Monthly Volume 53.djvu/597

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APPLETONS’

POPULAR SCIENCE

MONTHLY.

 

SEPTEMBER, 1898.



GEOLOGICAL WATER WAYS ACROSS CENTRAL AMERICA.
By Dr. J. W. SPENCER.

Introduction.—From the days of early discovery, adventurers and explorers have repeatedly sought for accessible routes across Central America. For more than half a century engineers have ransacked the dense mountain forests for easy passes through which to connect the two great oceans by water or by rail. The number of low passes which dissect the Cordilleras and plateaus between North and South America is much larger than is popularly known. Indeed, there are so many deep breaks in the plateau regions as to suggest that many of them at no distant date were water ways between the Atlantic and Pacific. On account of the narrowness of the Isthmus of Panama and the low altitude of the divide, this region has been most noticed as a possible geological passageway between the Antillean waters and the Pacific Ocean. But it has been discovered that other water ways across the American continent can be even more surely established, and that neither the narrowness of the Isthmus of Panama nor the lowness of the divide form any additional evidence of the late interoceanic connection.

The early Tertiary period—the time when water connection across Panama had been suggested—was so long ago that the land animals have completely changed their characteristics, and even the sea shells have been mostly transformed into more modern species; accordingly, the time has been sufficiently long for several subsequent changes in the physical barriers between the Atlantic and Pacific. Indeed, geological straits across the continent have existed at differ-