Maech 30, 1900.] 



SGIENGK 



515 



upon the mathematical work of Hertz, J. J. 

 Thomson and Heaviside, of the character of the 

 electrical waves which pass out from the vertical 

 wire at the sending station ; he calls attention 

 to the rational basis for Marconi's law, or rather 

 a modification of Marconi's law, that the range 

 of signalling in miles is proportional to the 

 product of the heights of the vertical wires at 

 the sending and receiving stations, and explains 

 why longer distance signalling is possible over 

 water than over land. Those who are inter- 

 ested in this matter will find Professor Fessen- 

 den's discussion instructive and interesting. 



Long distance wireless telegraphy seems to 

 be now almost within reach, with high sending 

 and receiving wires and with very powerful 

 electrical disturbances at the sending station, 

 very slight improvements in the sending and 

 receiving apparatus will likely carry the range 

 up to a thousand miles or more. 



W. S. F. 



CUBBENT NOTES ON PHYSIOGBAPHY. 

 lOWAN DRIFT. 



Continued studies of the drift of Iowa by 

 members of the State Geological Survey give 

 new details regarding the topographic differ- 

 ences between the three chief drift sheets 

 (Kansan, lowan and Wisconsin), indicative of 

 their diflerences of age. Calvin describes the 

 lowan drift sheet {Bull. Geol. Soc. Amer., x, 

 1899, 107-120) as forming a broad plain of long, 

 gently sweeping undulations, on which stream 

 erosion has in general done little work ; only 

 the main drainage lines, many of which follow 

 sags in the drift that are taken to indicate pre- 

 lowan valleys of erosion, are well defined ; 

 small lateral channels have been eroded only a 

 mile or so from the main valleys. In contrast 

 with this little carved surface, the Kansan 

 sheet, next south, was maturely and deeply 

 eroded before the lowan sheet was deposited. 

 The Kausan-Iowau interval is thought to have 

 been fifty times the post-Iowan period. About 

 the middle of the latter period is taken as the 

 date of the lobe of Wisconsin drift that enters 

 from Minnesota and overlaps both the lowan 

 and Kansan sheets. The surface of this lobate 

 area shows even more distinct signs of youth 

 than are found in the lowan area ; undrained 



depressions are of frequent occurrence on its 

 undulating prairies ; oxidation and leaching 

 have hardly begun ; stream erosion is insignifi- 

 cant. The value of topographical evidence as 

 indicating geological dates is seldom better 

 illustrated. 



The same author described ' a notable ride ' 

 from the driftless area of northeastern Iowa to 

 the lowan drift sheet, where the contrasts of a 

 maturely dissected upland of normal develop- 

 ment, and the broad swells and troughs of a 

 till plain are well presented (Amer. Geol., xxiv, 

 1899, 372-377). 



WESTERN AUSTRALIA. 



An account of part of western Australia by 

 Cadell (' Some geological features of the Coast of 

 Western Australia,' Trans. Edinh. Geol. Soc, 

 vii, 1897, 174-182) ascribes the absence of har- 

 bors to a recent slight elevation after prolonged' 

 denudation. The elevation is indicated by 

 raised beaches, now 10 or 15 feet above sea 

 level, one beach being from 12 to 18 miles 

 wide and reaching 25 miles inland. The 

 beaches lie on a low, flat plain of denudation, 

 monotonous and desolate, sloping impercep- 

 tibly to the sea. An inland excursion of seventy 

 miles was chiefly over a perfectly flat surface 

 of granite, clay slate and other rocks, strewn 

 with wind-worn pebbles and relieved by occa. 

 sional crystalline knobs which rise over its 

 prairie-like expanse. No mention is made of 

 incised valleys ; the few water courses of the 

 region, usually with dry beds, seem to lie 

 but little below the general level. The rocks 

 are as a rule deeply weathered ; water being 

 commonly found in wells at depths of 45 or 50 

 feet. The inland termination of the plain is 

 not described. The possibility of accounting for 

 such a plan by subaerial or by marine denuda- 

 tion is recognized, and a preference is expressed 

 for the latter agency in this case (although the 

 deep weathering of the rocks seems to be more 

 accordant with a subaerial history). A compar- 

 ison is made between this denuded lowland and 

 the flat pavement on which the Cambrian rocks 

 of northwest Scotland rest ; it is further sug- 

 gested that if the Australian plain were scoured 

 by glacial action, it would be ti-ansformed to 

 a hummocky surface, resembling the ' rough 



