EXPLANATION OF FORMATION OF INTERCONTINENTAL ZONE 87 



his expanded skull by the assumption of the " march e bipede " to which 

 he was compelled by the intense volcanic activity in Java, thus connect- 

 ing the advent of man with the advent of vulcanism.* 



t A broad zone of unfolded table-lands, often Archean but partly cov- 

 ered by flat rocks from eustatic transgressions, which have been since 

 a time long antecedent to the upfolding of these mountain chains un- 

 affected by orogenic forces, stretches south of these chains, including north 

 Africa, Arabia, India, Australia, and Guiana (see plate 14 a, 6, page 78), 

 and represents the central portion of the equatorial elevation which, as 

 tidal friction retarded the earth's rotation, became partially unsupported, 

 and, in sinking, 'furnished the northward thrust which has raised up 

 Alps and Antilles upon its flank, or, resisting collapse up to the strength 

 of its material, allowed the more plastic superficial strata to flow north 

 in mountain folds according to the acute suggestion of Reyer,j; that moun- 

 tain chains seem not like the effect of tangential thrust, but like the result 

 of the sliding of slightly plastic strata down a low slope under the in- 

 fluence of gravity. A first effect may have been the sinking of large 

 blocks at spots along the slightly unsupported slope of the flattening 

 ring forming the deep pockets so peculiar to all the Mediterraneans. 

 Then perhaps the gathering of sediments around the borders aided in 

 the formation of the mountain chains which surrounded the sunken 

 blocks. Then followed the general sliding or succession of slidings of 

 the whole series northward down the slope, forming the mountain chains 

 and island chains often circumjacent to the sunken blocks which belt 

 the earth along the Mediterranean zone, and causing all the volcanic 

 and seismic activity which is concentrated along the concavity of the 

 curves. 



This sliding might be carried down a very low slope, solicited, as it 

 were, by the constant stresses of the earth tides and occasional earthquake 

 vibrations, especially in soft and water-soaked strata recently emerged 

 from the sea. 



Finally came the sinking of great blocks of these chains where they 

 had come to rest on portions of crust unequal to their support, as where 

 the Apennines cross into Africa or the Caucasus sinks in the Pontus and 



* Am. Jour. Sci., 4th series, vol. iv, 1897, p. 237. 



t We present the following conjectural explanation in the indicative for brevity and directness, 

 noting that the more conservative idea that only the early outlines of these chains were dependent 

 on this position of the slope of the sinking ring is perhaps more defensible, and noting also that 

 the suggestion of this relation retains a certain plausibility apart from the success or our expla- 

 nations, 

 t Theoretische Geologie, 1888, p. 479. 

 Ursachen d. Deformationen und d. Gebirgsbildung, 1892. 

 Geologische Experimente, Heft iii, 1894, p. 9. 



