208 



SCIENCE 



[N. S. Vol. XXXIII. No. 841 



changes of chemical state in the hetero- 

 geneous material within the earth such that 

 increase of pressure in time produces in- 

 crease of density, and relief of pressure 

 produces decrease of density. 



The direct effects of erosion and deposi- 

 tion on temperatures in the underlyitog 

 material are such as to cause changes of 

 density opposite to those caused directly 

 by the change of pressure and probably 

 occurring later than those caused by 

 changes of pressure. 



Gravitation tends continuously to bring 

 about a readjustment to isostatic condi- 

 tions by producing a deep undertow from 

 a region of deposition to a region of ero- 

 sion. 



This undertow by virtue of heat pro- 

 duced by internal friction and by virtue of 

 surface compressive stresses in the horizon- 

 tal direction tends to raise the surface of 

 the neutral region between a region of 

 deposition and one of erosion. 



The phenomena of isostatic readjust- 

 ments by gravitation are complicated. 

 Actions involved at any one spot are a 

 function of the facts at manj^ other places 

 and of the facts of earlier ages. 



The material in the earth to a depth of 

 76 miles is weak lander the action of forces 

 applied for geologic ages. The effects of 

 gravitation predominate over those of other 

 forces to this depth. 



John F. Haytord 



THE MEBSHOjS' expedition TO THE 



CHARITY ISLANDS, LAKE EVRON 

 Foe several years the University of Mich- 

 igan Museum and the Michigan Geological 

 and Biological Survey have been cooperating 

 in a biological survey of the state. The sur- 

 vey has had a small annual appropriation for 

 this work, and has deposited the collections in 

 the museum, but the expeditions sent out from 

 the latter have nearly all been made possible 

 by gifts from persons interested in the prog- 

 ress of the work or in the institution. 



In the summer of 1910, Hon. W. B. Mer- 

 shon, Saginaw, Mich., placed in the hands of 

 the chief field naturalist of the survey, who is 

 also the head curator of the museum, a sum 

 sufficient to send a small party to the Charity 

 Islands in Saginaw Bay, for the purpose of 

 investigating the fauna and flora. 



The Charities comprise a group of three 

 small islands situated near the mouth of 

 Saginaw Bay. The largest of these. Charity 

 Island proper, contains about 650 acres, Little 

 Charity Island, the next largest, about 3 acres, 

 and Gull Island is a small projecting reef, 

 about a quarter of an acre in extent, that is 

 not usually shown on the maps. The group 

 is somewhat nearer the west coast than the 

 east. As plotted on the Lake Huron Coast 

 Chart No. 2, of the United States Lake Sur- 

 vey, the distances of the larger island (where 

 most of the work was done) from the main- 

 land are as follows : to Point Lookout, slightly 

 north of west, six and seven eighths miles; 

 from Caseville, due southeast, nine and five 

 eighths miles; from the end of Sand Point, 

 a little east of south, seven and three fourths 

 miles; from Oak Point, south of east, nine 

 miles. 



The islands are of interest biologically in 

 two ways. In the first place, as they have not 

 been connected with the mainland since gla- 

 cial times, the biota must have reached them 

 over a stretch of water at least as broad as that 

 which now separates them from the mainland. 

 In the second place, they are apparently upon 

 a migration route of many species of birds. 



The men engaged to do the work and the 

 groups to which they devoted most of their 

 time were as follows : W. W. Newcomb (but- 

 terflies and moths), N. A. Wood (vertebrates),- 

 A. W. Andrews (beetles), Frederick Gaige 

 (ants), C. K. Dodge (plants). The museum 

 and survey are greatly indebted to these men, 

 for they did the field work without other 

 remuneration than their expenses, and are 

 now preparing their results for publication. 

 Acknowledgment should also be made of the 

 assistance of the light-house board, Wash- 

 ington, T>. C, and Commander C. B. Morgan, 

 inspector of the eleventh light-house district, 



