June 23, 1893.] 



SCIENCE. 



343 



and drainage areas for the Rhone, Po, Danube, and Uruguay are 

 taken from a paper by John Murray in the Scottish Geographical 

 Magazine for February, 1887. The drainage area of the Nile was 

 measured by planimeter from the best maps obtainable. 



Discharge and Sediment of Large Rivers. 



GLACIATION IN PENNSYLVANIA. 



BY EDWARD H. WILLIAMS, JR., LEHIGH UNIVERSITY, SO. BETHLE- 

 HEM, PA. 



Owing to the difference of opinion regarding glaciation in this 

 vicinity, I have taken the subject for the out-door work of the 

 post-graduates in the mining course, during the past few months, 

 as their geological survey, and I make now a preliminary 

 statement of what has been found, without theorizing upon it in 

 any way, as the work is to be continued and extended to adjoin- 

 ing regions. 



The Lehigh University is situated on the north slope of what 

 is called The South Mountain, or the Durham and Reading Hills, 

 immediately back of South Bethlehem, Pa. The crest of the same 

 varies from 665 to over 900 feet above tide, at the point mentioned. 

 This is above the reach of glacial deposits by floating ice. To 

 the north lies the great valley bounded by the Blue Ridge, and 

 just north of this is a lower ridge of Oriskany sandstone in a ver- 

 tical position. The nearest portion of this sandstone is therefore 

 beyond the Blue Ridge. As the rocks of this ridge are mainly 

 barren, while the Oriskany sandstone carries the usual fossils, this 

 formation was taken as a test-rock, owing to the fact that the 

 rock called Potsdam sandstone sometimes weathers so as to great- 

 ly resemble rocks of other formations. ■ 



Professor Salisbury stated that he had found glaciated stones 

 500 feet above the Lehigh River, on the mountain back of the 

 University, and adduced that fact to refute the statement of Pro- 

 fessor Wright, that the ice failed to come as far south as Bethle- 

 hem. The height of the point noted was proof that the speci- 

 men had not been brought by water, and that the ice-sheet had 

 extended across the great valley. From this was deduced the 

 idea that there had been two periods of glaciation, and that the 

 one marked by the terminal moraine north of us, was the later of 

 the two. 



1 "Report upon the Physics and Hydraulics of the Mississippi Elver," by 

 A. A. Humphreys and H. L. Abbot, Philadelphia, 1861, p. 149. 



= "Eleventh Annual Report U. S. Geological Survey," Washington, 1891, 

 Part 11., p. 57. 



' Scottish Geographical Magazine, February, 1887, p. 76. 



< " Irrigation in Egypt," by J. Barols, translated by Major A. M. Miller, 

 Washington, 1889, p. 18. 



E " Hydraulics of Great Rivers," by J. J. Revy, New Yorli, 1874, p. 135. 



' " Report on the Irrawaddy Klver," by R. Gordon, Rangoon, 1880, Part III. 

 p. 25. 



' Special Consular Reports, House of Representatives, 51st Congress, 2d 

 D, Ex. Doc. 45, Part I., p. 269. 



To the south of that part of the mountain back of the Univer- 

 sity, lies a land-locked valley, so that there was no drainage 

 southward, except at high levels, during the time when the 

 bowlder clay was deposited and therefore there would be no cur- 

 rent to divert icebergs into that valley and cause a universal dis- 

 tribution of that clay, as there is to the north of the South Moun- 

 tain. 



The preliminary work shows that Oriskany pebbles and bowl- 

 ders are found at all altitudes over this mountain, and the great 

 majority of the smaller ones lie in a clay, which may be due to 

 the decomposition of the gneiss of the mountain; but which ex- 

 ists on the top of the highest part of the ridge These have been 

 traced into the Saucon Valley to the south as far as a line tun- 

 ning from Friedeneville to the second railroad cut south of Bin- 

 gen. South of that line we find the clays from the subjacent 

 limestones generally free from foreign stones, as far south as 

 Centre Valley, the southern part of the survey. North of that 

 line we have found four lines of glaciated material. In the val- 

 leys these run across all the formations from gneiss to limestone, 

 in lines generally parallel, and with a freedom of glaciated mate- 

 rial except in the lowest parts, where ice may have been present. 

 Oriskany bowlders are found of considerable size, and in some 

 parts abundantly. Only one of these lines has been traced fully, 

 and that runs from the north of Bingen and at an elevation of 

 about 300 A. T., across the Saucon Creek and Valley, and, pass- 

 ing south of Seidersville, has been followed to the summit of a hill 

 west of the latter place, and at an elevation of 720 A. T. 



It is comparatively easy to trace these lines, as the farms are 

 provided with wooden and wire fences, except where these lines 

 exist, and there the fences are of stone heaps, and the soil is 

 stony. Digging under these lines shows that they are resting on 

 rock in some oases, and on soil in others. 



It may be said that the ice went over the South Mountain. In 

 this case there has since been a great disintegration of the gneiss, 

 as the cuttings for the South Bethlehem reservoir show 25 feet of 

 rotten rock in some places. It may be said that these are evi- 

 dences of a older glaciation; but this older intrusion followed 

 exactly the lines of the later one, as can be seen by running aline 

 from the points in New Jersey noted by Prof essor Salisbury (Pat- 

 tenburg. etc.) to Seidersville, Pa., so that the advocates of a sin- 

 gle period can say that this was a sudden intrusion for a short 

 period followed by rapid retreat for twenty miles. 



This work is not sufficiently extended to furnish data for the- 

 orizing, and it will be extended in the future; but attention is 

 called to the fact that here exists a good field for observation, as 

 the rooks of the country (gneiss quartzite and limestone) cause 

 intrusive rocks from the Blue Ridge to be very prominent. 



INFLUENCE OF PARASITES ON OTHER INSECTS. 



BY G. C. DAVIS, AGRICULTURAL COLLEGE, MICH. 



From a philantrophio standpoint, it seems cruel to see one 

 class of insects preying upon another. The eager female para- 

 site is so vigilant in her search that one would think a subject of 

 her search could not escape till it had reached maturity; yet 

 strategy, mimicry, offensive odor, hairy and other coverings, and 

 many other peculiar and interesting methods of protection help 

 to shield and protect the invader from its insidious foe till out of 

 danger. In watching the ups and downs of the two from year 

 to year, about the only effect that is noticeable is that the para- 

 site generally holds the balance of power, though usually the bal- 

 ance is well equipoised. 



Viewed from an economic and practical side, the practice loses 

 its cruel aspect and is encouraged and fostered in many ways, as 

 it means an inexpensive control of many of our common pests. 

 There is little doubt but parasites do much more good than we 

 are wont to give tbem credit for. In a large share of the cases 

 of parasitism, about so many individuals of a species are para- 

 sitized each season, and the number left remains too small to pro- 

 duce serious damage. On the other hand, if the species had no 

 parasite to contend with, it would soon be numerous enough to 

 be a dreaded pest. 



Very often certain species do appear in greatly increased num- 



