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SCIENCE. 



[N. S. Vol. III. No. 73. 



my guess and the actual distance, but often- 

 times by the size of the rock when I reached it. 

 A stone which looked as large as a cabin at four 

 or five hundred yards would turn out to he 

 about as big as a bushel basket. I found much 

 difficulty in overcoming the tendency to exag- 

 gerate distance, though the Indians apparently 

 were not so troubled." In response to my in- 

 quiry, he further writes : ' ' When I got so I 

 could judge the distance with comparative ac- 

 curacy, it was simply that I had to accommodate 

 myself to the new ( to me ) size of rocks at 

 those distances." From which it is plain that 

 the newly determined distance by pacing did 

 not alter the apparent size of rock, the apparent 

 size is simply interpreted for a new distance 

 value. He says to himself, ' ' that appearance 

 means not as I might before have judged, but 

 so much more or less distance. ' ' In other words 

 there is here no judging from sense of accom- 

 modation or muscular sense of any kind, because 

 that is unaltered, the image of the thing seen be- 

 ing constant as to size and appearance. Distance 

 for Mr. Whitney seems to be purely a judgment, 

 more or less revised by actual pacings, of fixed 

 visual appearances. 



Another point on the perception of distance 

 was suggested by James (Psychology, II., 213): 

 " I cannot help thinking that anyone who can 

 explain the exaggeration of the depth sensation 

 in this case ( inverted vision ) will at the same 

 time throw much light on its normal constitu- 

 tion." This suggests whether bats which hab- 

 itually hang head downwards would not have 

 distance lengthened by erect vision. I do not 

 know whether this could be tested by bringing 

 certain foods to the attention of such animals 

 at varying distances for inverted and erect vis- 

 ion. I found by some simple experiments upon 

 myself and also upon a friend that lying down, 

 with the head in horizontal position, distance 

 was shortened, but I was not able to test at 

 what angle toward inverted vision distance 

 first began to lengthen. If not already tried, it 

 might be useful for some of our psychological 

 laboratories to set up a tackle, so that a person 

 might be revolved through the whole circle, 

 and the effect on perception of distance noted 

 at all angles. It would also be well to test 

 whether inverting the object looked at dis- 



turbed the sense of distance. I got no result 

 in this matter by looking at objects at the end 

 of a long hall. Hieam M. Stanley. 



Lake Foeesx, III., April 27. 



THE MAMMOTH BED ^T MOEEA, PA. 



To THE Editor of Science : The following 

 interesting section was found on the glaciated 

 outcrop of the Mammoth (E) bed at Morea, Pa. , 

 within one mile of the farthest southern limit of 

 glaciation, and from 20 to 26 miles south of the 

 moraine of Lewis and Wright. The measures 

 are nearly vertical and form a narrow and deep 

 basin. A section taken on the bed gave : 



(a) Till of sandy, clayey nature, with burdea 

 of Pottsville conglomerate and varying sand- 

 stones, and with irregular lenticular patches of 

 clean reddish clay of small extent. The solid 

 burden is angular and sub-angular, and not 

 polished nor striated. In some cases boulders 

 5 feet thick occur. Total thickness, 6 to 10 feet. 



(b) Crushed anthracite, bright and firm, 

 shipped to market. This is readily scraped up 

 with the fingers. In places to the north hun- 

 dreds of tons of this crushed coal have been sold. 

 When we realize that this is under a sandy till 

 we can estimate the comparative recency of 

 glaciation. In some places this layer will reach 

 18 inches in thickness. 



(c) Rotten anthracite with angular specks of 

 firm slate from coal. Thickness f inches. 



(d) Sandy clay, usually grayish, but some- 

 times clear red or yellow. It bears rolled and 

 angular quartz and slate pebbles, pieces of an- 

 thracite, but little anthracite dust. Thickness 

 1 inch. 



(e) Crushed anthracite, firm and bright, like 

 (b). Thickness \ to f inches. 



(f) The glaciated surface of the outcrop of 

 the bed. Soft and fully rotted so as to be dull, 

 like black chalk, and easily cut by the finger- 

 nail. Thickness | of an inch. 



(g) Solid and bright anthracite of the bed. 

 On comparing unglaciated or protected out- 

 crops we find (f ) measuring many feet in depth. 

 We find here that the amount of decomposi- 

 tion of solid coal since glaciation is i of an inch. 



The presence of the layer (d) is peculiar be- 

 tween two layers of crushed anthracite which 

 are bright and fresh. 



