876 PRINCIPLES OF STRATIGRAPHY 



valleys the permanent and periodical rivers were loaded with the 

 new ash to such an extent as to form viscous streams, which, how- 

 ever, had great powers of erosion, on account of the steep slope of 

 the declivities down which they flowed. The hottoms and sides of 

 the gorges were deeply grooved by the sand carried down in this 

 manner by the flowing water. 



"During the great eruptions the ejected material was drifted into 

 large beds in the gorges extending radially down the Soufriere 

 [on St. Vincent Island]. The massing of material was most im- 

 portant in the gorge of the Wallibou River on the west, and in 

 that of the Rabaka River on the east, side of the island. In these 

 gorges the bed of new material reached a thickness of from 60 

 to 100 feet. This enormous amount of material was almost entirely 

 washed out of the gorges during the first rainy season following 

 the eruptions of 1902. Not less than 150,000,000 cubic feet of 

 ashes have been washed out of the Wallibou gorge itself, without 

 taking into account the thousands of cubic yards of fresh ash re- 

 moved from the watershed of the river during the same period. 

 All this material was, of course, transported directly to the ocean." 

 ( Ho vey- 1 8 :5(5o.) 



FORMATION OF THE LAVA. 



Since it is very unlikely that at any point within the earth's crust 

 the temperature is sufficiently high to melt rocks (see Chapter I) 

 at the increased fusing point caused by the increase in pressure 

 downward, it follows that some other factors must be taken into 

 consideration in explaining the liquefaction of rock. We must, 

 therefore, seek either for causes producing an increase of tempera- 

 ture, or for such producing a decrease of pressure. The former 

 may be found in the energy liberated by radio-active substances, 

 such as are found in practically all the rocks of the earth's crust, as 

 well as in the water and the air. Since, says Chamberlin (3:(57p), 

 "radio-activity increases as we go from air to water, from water 

 to sediment, and from sediment to igneous rock, it might be inferred 

 . . . that radio-activity would be found to reach its maximum 

 concentration in the heart of the earth, and certainly that the deeper 

 parts would be as rich as the superficial ones." This, however, 

 would imply a more rapid increase in temperature than observation 

 indicates. Strutt (quoted by Chamberlin) has computed that, if 

 the quantity of radio-active substances known to exist in surface 

 rocks is also found throughout the rocks of the upper 45 miles 



