52 THE BUILDING OF AN ISLAND. 



product idtiviatcly of igneous rocks, the other extracted from sea-water by 

 living agencies. 



2. That, although ultimately in the main a product of igneous rocks, it 

 has been laid down in the sea in regular strata. 



3. That the supply of material has apparently been so abundant and so 

 continuous as to allow only of a small contemporaneous deposition of lime- 

 stone by the sea creatures, yet that there are, nevertheless, some scanty re- 

 mains of such limestone deposits, and that these contain distinct evidences of 

 their origin in the sea. 



4. That after their deposition in the sea the strata have been greatly 

 altered by heat and water, so that they have for the most part taken a crys- 

 talline form. 



5. That they have also undergone some other remarkable changes, such 

 as attaining in many of the beds the variolitic character, the tendencv to split 

 in certain directions, known as jointino; and especially in this connection, in so 

 far as the slaty rocks are concerned, the ac(|uisition of cleavage. 



6. That while these changes were going on, or at all events since the de- 

 position of the materials, the whole mass of strata was forced up bv pressure, 

 from about north-northeast, into parallel waves or ridges, whose form has again 

 been affected by pressure crosswise to the above-named direction. 



-. That the crests of these waves were eaten awav through a vast period 

 of time by incessant attacks from the sea along the land edges and by the rains 

 and the consequent streams over the surface, so that at last thev were planed 

 down, perhaps so far even as to leave an approximately level surface, present- 

 ins evervwhere the edijcs of the strata. 



<S. That the land so planed down then sank under the sea and received 

 on the upturned edges of the strata, during another vast period of time, the 

 deposits which make up our limestone and marl formation. 



9. That having received these large deposits on the upturned edges of 

 the strata, the whole mass was once more forced up, bringing them above the 

 surface of the water along with it. 



10. That both formations have since then, and partly also during the lift- 

 ing ])rocess, l)een acted on bv the sea and by the rains and streams, so as to 

 have their surfaces carved into the forms we now see, a subject, however, 

 which' has so large a scope that it will be well to reserve it for separate study. 



Before proceeding to that subject we mav take a brief look at the igneous 

 rocks which have been intruded from below into the older formation but have 

 never, so far as is known to the present writer, reached so high or been in- 

 truded so late as to show themselves in the newer or limestone formation. 



