FORM OF THE CONTINENTS— WATTS 187 



from earlier rocks give very little idea of what had gone before, and 

 no evidence whatever as to the beginnings of life. 



But, from Cambrian time onward the chain of life is continuous and 

 unbroken. Type after type has arisen, flourished, and attained do- 

 minion. Some of them have met extinction in the heyday of their 

 development ; others have slowly dwindled away ; others, again, have 

 not finished their downliill journey, or are still advancing to their 

 climax. 



Study of the succession of rocks and the organisms contained in 

 them, in every case in which evidence is sufficiently abundant and 

 particularly among the vertebrates and in the later stages of geological 

 history, has now revealed that the great majority of species show 

 close affinities with those which preceded and with those which fol- 

 lowed them; that, indeed, they have been derived from their prede- 

 cessors and gave origin to their successors. We may now fairly claim 

 that paleontology has lifted the theory of evolution of organisms from 

 the limbo of hypothesis into a fact completely demonstrated by the 

 integral chain of life which links the animals and plants of today with 

 the earliest of their forerunners of the most remote past. 



Further, the rocks themselves yield proof of the geographical 

 changes undergone by the earth during its physical history; and 

 indicate with perfect clearness that these changes have been so closely 

 attendant on variation in life, and the incoming of new species, that 

 it is impossible to deny a relation of cause and effect. 



Indeed, when we realize the delicate adjustment of all life to the 

 four elements of the ancients which environ it, air, water, earth, 

 and fire, to their composition, interrelationships, and circulation, 

 it is perhaps one of the most remarkable facts established by geology 

 that, in spite of the physical changes which we know to have oc- 

 curred, the chain of life has never snapped in all the hundreds of 

 millions of years through which its history has been traced. 



The physical changes with which Lyell and his successors were 

 most closely concerned were, firstly, the formation of stratified 

 rocks on horizontal sea floors, situated in what is now often the 

 interior of continents, far removed from the oceans of the present 

 day, and thus indicating important and repeated changes in the posi- 

 tion of land and water ; and, secondly, the deformation of these flat 

 deposits till they were rucked and ridged to build the mountain 

 ranges. 



Before and since Lyell's time geologists have devoted themselves 

 to working out the exact and detailed succession of these stratified 

 rocks, translating their sequence into history and their characters 

 into terms of geography, the succession of physical conditions 

 prevailing at the time of their formation. Further, although ani- 



