P OP ULAR MIS CELL ANY. 



509 



toward the hatching-grounds of their par- 

 ents, so that two years seem to be required 

 to complete the migration cycle. Tlie 

 methods of prevention proposed are the 

 cultivation and preservation of forest-trees ; 

 the protection of the prairie-grass till the 

 appropriate time for destroying the young 

 insects by fire ; and the protection of in- 

 sect-catching birds. 



A New Whe.it-Fnnjins in California. 



Early in Mai-ch of the present year the 

 young wheat in certain districts of Califor- 

 nia began to exhibit on its expanded leaves 

 yellowish-white patches of fungous growth. 

 This peculiar species of " rust " or " mil- 

 dew " appears to be new to California, and 

 has been recognized by Mr. H. W. Hark- 

 ness, of the San Francisco Microscopical 

 Society, as the Erysiphe graminis of De 

 Candolle. According to Mr. Harkness, the 

 fungus appears on the expanded leaves in 

 felt-like patches, from one-sixteenth to one- 

 half inch in length, following the longest 

 diameter of the leaf equally on both sides. 

 It adheres with great tenacity, though, on 

 examining sections of the leaf and fungus, 

 no suckers are apparent. The leaf, at a 

 short distance from the culm, soon turns 

 brown and dries. In the earlier stages the 

 mycelium is observed creeping over the sur- 

 face, its filaments overlying one another 

 until it forms a felted mass. To what ex- 

 tent the wheat will be damaged, it is as yet 

 impossible to say. Adhering, as it does, 

 closely to the plant, it doubtless appropri- 

 ates the juices needed for maturing the 

 grain, at the same time excluding air and 

 sunlight from the tissues. Its visible ef- 

 fect is a weakening of the stalk, thus favor- 

 ing decay. 



A New Measure of Geological Time. 



The amount of solid matter abraded from 

 the land and carried to the sea as sediment, 

 or in suspension, has often been estimated 

 by geologists, and the importance of this 

 suspended matter as an agent of geological 

 changes has been fully recognized. But 

 less attention has been bestowed upon the 

 soluble matter washed out of the earth by 

 every fall of rain and added to the waters 

 of the ocean. This subject has been studied 

 by Mr. T. Mellard Reade, whose results, as 



I set forth in his presidential address to the 

 Liverpool Geological Society, we find sum- 

 marized in the Nineteenth Century as fol- 

 lows : The author's first problem was to 

 estimate the total quantity of solid material 

 removed in the course of one year, by the 

 solvent action of rain, from the entire sur- 

 face of England and Wales, supposing the 

 mean rainfall to be thirty-two inches. It 

 is worthy of note that the variation of rain- 

 fall in different parts does not affect the 

 quantity of dissolved matter to anything 

 like the extent that might have been an- 

 ticipated. True, the hilly districts of the 

 west, in Cumberland, Wales, Cornwall, and 

 Devon, intercept a large quantity of rain ; 

 but, then, these collecting-grounds are com- 

 posed of old rocks, ranging from Cambrian 

 to Carboniferous ; and such rocks are, to a 

 great extent, insoluble. On the other hand, 

 in the southern and eastern counties the 

 rainfall is much less than in the west ; but, 

 then, the rocks belong generally to Second- 

 ary and Tertiary formations, and are toler- 

 ably soft and soluble. A kind of compen- 

 sation is thus established, the total quantity 

 of solid matter carried off in solution in a 

 given time being much the same in one 

 river as in another. Roughly speaking, it 

 may be said that where the rainfall is great- 

 est the solubility is least ; where the rain- 

 fall is least the solubility is greatest. It is 

 needless to follow the details of the calcu- 

 lation by which the author is finally led to 

 the conclusion that about 8,370,630 tons 

 of solids are annually removed in solution 

 by the rivers of England and Wales. Dis- 

 tributing the denudation equally over the 

 country, the total area being 58,300 square 

 miles, we obtain a general lowering of the 

 surface to the extent of .000077 of a foot in 

 a single year ; in other words, it would re- 

 quire 12,978 years to reduce the surface of 

 England and Wales by one foot through 

 the solvent action of rain alone. Fewer 

 data exist for extending this interesting 

 inquiry to the Continent of Europe, and 

 fewer still when we pass to other parts of 

 the world. But, making the best of avail- 

 able data, and proceeding on the principle 

 that " Nature, on the whole, averages the 

 results," Mr. Reade feels justified in assum- 

 ing provisionally that about one hundred 

 tons of rocky matter will be dissolved by 



