LAND CONNECTION BETWEEN AFRICA AND AMERICA 85 



the fragments torn from the throats of volcanic pipes have been 

 rounded by attrition, and assume the characteristics of water- 

 worn bowlders. In crush-breccias at Kuysna I have found rounded 

 bowlders of exactly the same shape formed on the very spot from 

 which they have been broken. The accounts of crush-breccias 

 from the Isle of Man and Canada bear out the same view, namely, 

 that rock-fragments can be rounded by simple dry friction. This 

 point is important as the presence of apparently water-worn 

 bowlders in volcanic agglomerates, such as those of the Kimberl)' 

 diamond pipes, has frequently been adduced as evidence of water- 

 action. 



The comparative coolness of these volcanic eruptions is remark- 

 able, and is such that in some cases, where fossihferous strata con- 

 tribute to the fragments in the volcanic pipe, the structure of the 

 remains are as fresh as in the parent rock. In Scotland Sir A. 

 Geikie records a vent at EHe Neck in which there are fragments 

 of crinoidal Hmestone which show no trace of metamorphism, 

 and their crowded organisms are as clearly recognizable as in pieces 

 of Hmestone from a quarry.^ In Kimberly the fragments of shale 

 in the blue mass are quite fresh, and blocks containing fossil fish 

 are as unaltered as if they had been procured from their original 

 resting-place. 



The temperature, however, was greater in other cases; for 

 instance, Branco records blocks of middle Lias marly clay from 

 the agglomerate in the Schleursbach volcano in Swabia, which 

 have been baked and the included belemnites turned to white 

 marble.^ In the far south, Philhpi^ describes blocks of granite 

 entangled in lava on the top of the Saussberg; the ferro- 

 magnesian minerals are melted, and the lava occupies the space 

 they once filled by a sort of pseudomorphism, while the quartz 

 and felspar remain intact. These blocks may have been derived 

 from the surface of the ice-cap which once extended over the Sauss- 

 berg, but the prolonged heating of the blocks, sufficient to melt 



I" Geology of Eastern Fife," Memoirs of the Geological Survey of Scotland (Glas- 

 gow, 1902), p. 241. 



2 Swabiens I2§ Vulcan-Embryonen (Stuttgart, 1894), p. 546. 



3 Verdffentlichungen des Instituts fiir Meereskunde, Heft 5, 1903, p. 126. 



