1867.] Ice Marks in North Wales. 33 



lead to the supposition that this means of transit will ever be very- 

 much extended. Where practicable, river navigation appears to be 

 extensively used, and the success or otherwise of the works at 

 present under construction with the view of opening up the navi- 

 gation of the Godavery, will probably determine whether or not 

 similar operations shall be carried out on other rivers. There is 

 also no doubt that by the introduction of an improved class of 

 steamers many rivers might successfully be navigated, which contain 

 too small a depth of water for the majority of the vessels hitherto in 

 use; three such steamers, calculated to draw only 12 inches of 

 water, are now in course of construction for the river Godavery. 

 Should they prove * successful on that river, it is not unlikely that 

 they will be followed by others on the same plan for employment 

 on various streams hitherto not navigated by steam, and on which 

 only vessels of very shallow draught could be employed. With 

 respect to railways, it is not probable that any very great extension 

 of the present system of high-cost lines will be sanctioned, except 

 where they may appear necessary for political or military purposes, 

 and we look rather to a development of the principle of light rail- 

 ways, which may readily be laid down along existing lines of road, 

 and ultimately perhaps, when the traffic has become sufficient to 

 justify the expense in' a commercial sense, they might be completed 

 substantially so as to unite with the existing system of high-speed 

 railways, just as it is customary to make a fair-weather road in the 

 first place, and afterwards complete it, by bridging and metalling, as 

 a first-class road. 



IV. ICE MAKES IN NOKTH WALES. 



(With a Sketch of Glacial Theories and Controversies.) 



By Alfred E. Wallace, F.E.G.S., F.Z.S., &c. 



One of the most interesting branches of modern geology, and 

 that on winch recent researches have thrown most light, is the 

 inquiry into the exact modes by which the present surface of the 

 earth has been produced. When we see a vertical precipice, a deep 

 chasm, or huge masses of shattered rock, our first impression is to 

 impute these effects to some violent convulsions of nature, such as 

 volcanic eruptions, earthquakes, or floods. It is, however, now 

 generally admitted that such causes have had, for the most part, 

 little if any effect in modifying the surface, except when many 

 times repeated during long periods of time ; and it is every day 

 vol. rv. r> 



