50 ALTERATION IN THE 



horizontal base which subtended the transition strata 

 of slate when they were deposited was only about 

 twice the extent of base which now subtends them, 

 that therefore the strata of gneiss were deposited 

 upon a globe, the magnitude of which was greater 

 than that upon which the transition strata of slate 

 were deposited, and because of this the strata of 

 gneiss suffered a greater contraction of base than 

 the transition strata of slate while adjusting them- 

 selves to the nucleus of a globe which, since their 

 formation, had constantly diminished in magni- 

 tude? 



77. If so, what was the magnitude of the globe 

 when the transition strata of slate were deposited ? 



78. The alterations that have taken place in the 

 position of strata since they were deposited have 

 been referred by geologists to the intrusion of igneous 

 matter into the crust of the earth. The undulations 

 of the strata are supposed to have been induced by 

 that lateral pressure which the adjacent rocks would 

 undergo when a disruption of the strata took place 

 in the formation of the fissure through which the 

 igneous matter was discharged. The strata repre- 

 sented in Fig. 1 4 have by their inflections suffered 

 a contraction of horizontal base, equal in extent to 

 four miles and a half. This contraction of the base 



