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profound depths of the ocean, the former
→mantle
may not have been
Admitting then that
→such rocks as
gneiss, mica-schist, granite, diorite,
were once necessarily covered up, how can we account for the
and
areas of such rocks in many parts of the world, except on the belief that they have subsequently been completely denuded of all overlying strata? That such extensive areas do exist cannot be
the granitic region of Parime is described by Humboldt as being at least nineteen times as large as Switzerland. South of the
Boué colours an area composed of
rocks
→as
equal to that of Spain, France, Italy, part of Germany, and the British Islands, all conjoined. This region has not been carefully explored, but from the concurrent testimony of travellers, the granitic area
very
thus, Von Eschwege gives a detailed section of these rocks, stretching from Rio de Janeiro for 260 geographical miles inland in a straight line; and I travelled for 150 miles in another
and saw nothing but granitic rocks. Numerous specimens, collected along the whole coast from near Rio Janeiro to the mouth of the Plata, a distance of 1100 geographical miles, were
me, and they all belonged to this class. Inland, along the whole northern bank of the Plata I saw, besides modern tertiary beds, only one small patch of slightly metamorphosed rock, which alone could have formed a part of the original capping of the granitic series. Turning to a well-known region, namely, to the United States and Canada, as shown in Professor H. D. Rogers's beautiful map, I have estimated the areas by cutting out and weighing the paper, and I find that the metamorphic (excluding
and granitic rocks exceed, in the proportion of 19 to
→12.5, not only the true coal measures, well known to be here developed in extraordinary force, but likewise the Umbral series, which together compose
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