330 Air-Pollution by Chemical Works. [July, 



Whether we measure the relative lapse of time occupied by the 

 successive events of Geological History by the known facts of the 

 accumulation of deposits, or by the comparative changes which have 

 occurred in the life of successive periods, we are led equally to infer 

 that the rate of geological change has been more rapid in the 

 later than in the earlier geological periods, and that that rate has 

 increased progressively from the earliest to the latest times. 



Such an inference, though it may at first sight seem here- 

 tical, is in reality but the natural result of those conditions of the 

 earth's surface which the most orthodox geologists regard as cha- 

 racteristic of successive periods. A greater uniformity of climate 

 and of surface in the earlier Palaeozoic periods than at the present 

 day has long been considered the legitimate inference to be drawn 

 from the thick masses of uniform deposits spread over large areas, 

 and containing species of fossils possessing an enormous geographical 

 distribution. In ascending the geological scale the deposits gradu- 

 ally become more differentiated, and the fossils belong to species 

 which had a more restricted geographical range ; these differences 

 are usually and properly regarded as the result of greater diversity 

 of climate and surface-configuration during the later periods, and 

 these more diversified conditions must have been accompanied by 

 a greater rapidity in the rate of geological chaoge, if for no other 

 reason than that there were a greater number of centres of change, 

 acting and reacting on each other. 



IV. AIE-POLLUTIOX BY CHEMICAL WOBKS. 



A MANTjFACTrKER, having realized his primary object of making 

 what he can out of the materials which pass under his hands, and 

 having utilized all that he deems valuable in them, finds there is yet 

 another need to be fulfilled ; he must get rid of his refuse, and that 

 as speedily as possible. Our present object is to watch this latter 

 operation, and, losing sight of the beautiful or useful results of his 

 work, to direct our attention to what is waste or refuse, and inquire 

 how he disposes of it. When this is solid and bulky, it must be 

 removed at the cost of much labour, and a place must be provided 

 where it can be deposited. When the refuse is a liquid, the pro- 

 cess of getting rid of it is generally less expensive ; it will flow away 

 in the water-courses if only proper drains and passages are provided. 

 When the refuse is gaseous, this process of removal is easier still ; 

 no passages need be cut, no culverts nor bridges built, the vapour 

 can be allowed to pass into the air, and is blown away. 



In each of these cases the manufacturer's object is attained ; he 

 is rid of the refuse, and has room for renewed work. Unfortunately, 



