﻿264 Canadian Record of Science. 



ill the ci>urse of a human lifetime, it is evident that an enormous length 

 of time was required for the accumulation of these strata, and when it 

 is learned that this system is but one of a dozen or more which succeed 

 one another in their order, and whose complete sequence is required to 

 unfold the story of the earth, we apprehend in some faint way the 

 abyss of geological time, which in its turn is a nothing compared with 

 the former time when the planets of our solar system were being 

 brouglit forth in their order, but the earth as yet was not. 



It is the aim of this little book of Professor Heilprin's to present 

 briefly and in popular form the main outlines of the earth's history 

 and to explain the play of the forces by which this history has been 

 recorded. It is quite elementary in chai'acter, being intended, as the 

 preface informs us, " for classes in high schools and colleges, and also 

 for the large increasing number of lay readers who are desirous of 

 knowing more about the formation, structure and development of the 

 earth on which they live." 



The earlier chapters describe a few commonest rocks which make up 

 the earth's crust, consisting of the igneous rocks, which owe their origin 

 to fire, and the aqueous or sedimentary rocks, which are produced 

 through the agency of water ; the latter, in their fossil ripple marks, 

 raindrop markings and impressions of footprints, presenting striking 

 testimony to the similarity of ancient conditions of deposition to those 

 which obtain along the sea-coasts of the present world. 



The lessons taught by the mountain chains of the earth's crust, with 

 their bent and dislocated strata, their deeply cutting streams and 

 slowly creeping glaciers, are then explained, and a chapter is devoted 

 to volcanoes and the causes of volcanic action, a class of phenomena 

 which, although often local, have in some parts of the earth's surface a 

 wide-reaching influence, as in Idaho and the adjacent states, where 

 floods of lava, welling up through fissures, have covered a region 

 equal in area to France and Great Britain combined, or in India, where, 

 in the Deccan, an area of 200,000 square miles is covered with lava 

 flows having in places an aggregate thickness of 6,000 feet ; or in what 

 is perhaps a still more remarkable district, namely, East Africa, where 

 similar enormous lava plains are cut across by faults or dislocations, 

 giving rise to precipices in some cases a thousand feet or more in height, 

 and which along one line result in the formation of an enormous rift 

 valley, a southerly continuation of that in which lies the River Jordan 

 and the Dead Sea. 



Corals and coral islands form the subject of another chapter, a sub. 

 ject with which will always be associated the names of the two great 

 naturalists, Darwin and Dana, and one upon which Professor Heil- 

 prin's studies in Florida and the Bermudas enable him to speak with 

 authority. 

 The treatment of these subjects leads naturally to the following 



