Geology and Mineralogy. 333 



fresh water was to transform the pi*eviously brackish lakes and 

 saline bays into fresh-water lakes and estuaries. But the result, 

 which it was the special purpose of the communication to bring out, 

 was the destruction of the salt-water fauna and the substitution 

 of fresh-water and mud-loving fauna over an immense area. 

 During the recent year an important industry of the gulf coast 

 about the outlets of the lakes mentioned was oyster fishing, but 

 the oyster beds all along the coast have been injured and in many 

 cases destroyed. The sea-fishery region has also been ruined, and 

 the pickerel and other characteristic fishes of the Mississippi may 

 now be taken where four months ago only salt-water forms were 

 found. This transformation in the fauna of the region is of im- 

 mense economic importance. Valuable industries have been de- 

 stroyed ; prices of standard commodities in New Orleans and 

 other Southern cities have been affected. Of even greater scien- 

 tific interest is the transformation, for it illustrates a transition 

 from a marine to a fresh-water fauna over hundreds of square 

 miles effected within a few weeks. Hitherto the geologist em- 

 ployed in the lower Mississippi region has been puzzled to account 

 for sudden transitions from fresh-water to salt-water deposits, and 

 vice versa ; but there is here a modern example of as wide extent 

 as in all those which have hitherto embarrassed the student. 



The reading of geological papers was continued before the 

 American Association then in session. A list of the papers is 

 given beyond, on pages 339, 340. 



2. Making of Icebergs. — Mr. Hbnkt B. Loomis, of Seattle, was 

 at the Muir glacier for nearly seven weeks this summer, with Prof. 

 John Muir. In a description of the visit (which mentions the 

 unfortunate feature of 20 days of almost continuous rain) he gives 

 the following account of the making of icebergs at the terminal 

 wall of the glacier. — Blocks of ice, some of them of enormous size, 

 fall off from this wall at frequent intervals. The falling of the 

 bergs is very irregular ; at times a berg is discharged as often as 

 every five minutes, at another time you may wait an hour with- 

 out seeing one fall. On one day, during twelve hours, we counted 

 129 thundering reports, loud enough to be heard at camp, a mile 

 or more from the falling bergs. During some days and nights, 

 especially during a heavy rain, we were reminded of a cannon- 

 ade or thunder-storm, and the ground beneath us seemed to trem- 

 ble. Sometimes a huge block breaks off, crumbles into a million 

 fragments, and, leaping like a catract, falls gracefully into the bay 

 with a long thundering noise, scattering around the white and 

 mealy spray which glistens in the sunlight, and making the water 

 below boil with foam. Another enormous block is discharged, 

 and, without breaking, sinks in an upright position into the water, 

 causing a low, thundering noise; then it rises again, sometimes 

 250 feet, even with the top of the wall of the glacier, while the 

 water rolls off its top like a cascade ; then the berg topples over 

 gracefully on its side and plunges into the water with a heavy, 

 thundering roar, like the sound of artillery or of thunder, and the 



