| → with great boulders, crossing the Portillo valley, which there can hardly be a doubt once formed a huge moraine; and Mr. D. Forbes informs me that he found in various parts of the Cordillera, from lat. 13° to 30° S., at about the height of 12,000 feet, deeply-furrowed rocks, resembling those with which he was familiar in Norway, and likewise great masses of detritus, including grooved pebbles. 1869 |
| about 800 feet in height, crossing a valley of the Andes; and this I now feel convinced was a gigantic moraine, left far below any existing glacier. 1859 1860 |
| with great boulders, crossing the Portillo valley, which there can hardly be a doubt once formed a huge moraine; and Mr. D. Forbes informs me that he found in various parts of the Cordillera, from lat. 13° to 30° S., at about the height of 12,000 feet, deeply-furrowed rocks, resembling those with which he was familiar in Norway, and likewise great masses of detritus, including grooved pebbles. 1872 |
|
| → from 1859 1860 1861 1869 1872 |
| former glacial action, in huge boulders transported far from 1866 |
|
| → formerly 1869 |
| at one time 1872 |
|
| → It follows from 1869 |
| According to 1872 |
|
| → but that at much longer intervals the cold, 1869 |
| and these at long intervals are extremely severe, 1872 |
|
|
a vast mound of
→with great boulders, crossing the Portillo valley, which there can hardly be a doubt once formed a huge moraine; and Mr. D. Forbes informs me that he found in various parts of the Cordillera, from lat. 13° to 30° S., at about the height of 12,000 feet, deeply-furrowed rocks, resembling those with which he was familiar in Norway, and likewise great masses of detritus, including grooved pebbles. Along this whole space of the Cordillera true glaciers do not now exist even at much more considerable heights.
south on both sides of the continent, from lat.
to the southernmost extremity, we have the clearest evidence of former glacial action, in
boulders transported far
→from
their parent source. |
|
| From these several facts, namely from the glacial action having extended all round the northern and southern hemispheres— from the period having been in a geological sense recent in both hemispheres— from its having lasted in both during a great length of time, as may be inferred from the amount of work effected— and lastly from glaciers having recently descended to a low level along the whole line of the Cordillera, it
→formerly
appeared to me that we could not avoid the conclusion that the temperature of the whole world had been simultaneously lowered during the Glacial period. But now Mr. Croll, in a series of admirable memoirs, has attempted to show that a glacial condition of climate is the result of various physical causes, brought into operation by an increase in the
of the
orbit. All these causes tend towards the same end; but the most powerful appears to be the
of the
of the orbit upon oceanic currents.
→It follows from
Mr.
cold periods regularly recur every ten or fifteen thousand years;
→but that at much longer intervals the cold,
owing to
|
