Tom Swift and His Big Tunnel, or, the Hidden City of the Andes by Victor [pseud.] Appleton
page 23 of 219 (10%)
page 23 of 219 (10%)
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"A snag in the shape of extra hard rock," replied the
tunnel contractor. "Briefly, Paleozoic rocks make up the eastern part of the Andean Mountains in Peru, while the western range is formed of Mesozoic beds, volcanic ashes and lava of comparatively recent date. Near the coast the lower hills are composed of crystalline rocks, syenite and granite, with, here and there, a strata of sandstone or limestone. These are, undoubtedly, relics of the lower Cretaceous age, and we, or rather, my brother, states that he has found them covered with marine Tertiary deposits. "Now this Mesozoic band varies greatly. Porphyritic tuffs and massive limestone compose the western chain of the Andes above Lima, while in the Oroya Valley we find carbonaceous sandstones. Some of the tuffs may be of the Jurassic age, though the Cretaceous period is also largely represented. "Now while these different masses of rock formation offer hard enough problems to the tunnel digger, still we are more or less prepared to meet them, and we figured on a certain percentage of them. Up to the present time we have met with just about what we expected, but what we did not expect was something we came upon when the tunnel had been driven three miles into the mountain." "What did you find?" asked Tom, who knew enough about geology to understand the terms used. Mr. Damon did not, however, and when Mr. Titus rolled off some of the technical words, the drug investor softly murmured such expressions as |
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