abstracts: geology 221 



has been poorlj' drained, the iron stain immediately under the bhxck soil 

 has been leached away and the deposit has an ashen-gray, almost white 

 appearance. 



The thickness of the loess is fairly constant for each drift sheet on 

 which it rests. On the upland of the Illinoian till it ranges from 20 to 

 30 feet and averages 24 feet. In two localities this older and thicker 

 loess was seen to contain fossil land snails. In each of these places the 

 loess is slightly calcareous. On the Wisconsin drift the loess averages 7 

 feet thick, but it varies considerably. On the older Wisconsin terrace 

 much of the surface is covered 3 or 4 feet deep by material which in every 

 way resembles the loess, except that in places it contains a small percent- 

 age of fine sand. 



The greater part of the loess outside the limit of the Wisconsin drift 

 must be older than the Wisconsin till, since a considerable thickness also 

 underhes the later till. It is a suggestive fact that the buried loess is 

 nowhere known to reach a thickness which when added to the average 

 depth of the loess on the Wisconsin till would exceed the average depth 

 of the deposit on the Illinoian till. W. C. Alden. 



GEOLOGY.^ — The mud lumps at the mouths of the Mississippi . Eugene 

 Wesley Shaw. U. S. Geological Survey Professional Paper 85-B. 

 Pp. 27, views and sections. 1913. 



The territory wdthin a mile or two of each of the mouths of the 

 Mississippi is characterized by large swellings or upheavals of tough blu- 

 ish-gray clay, called "mud lumps." Many of these rise just offshore and 

 form islands an acre or more in extent and 5 or 10 feet high, but some do 

 not reach the water surface. They rise and subside at irregular rates, 

 some of them suddenly. 



Certain features of the Delta suggest that it is affected by a process 

 which heretofore seems not to have been suspected, namely, a bodily 

 flowage toward the sea. The surface receives a new layer of sediment at 

 each flood, but its altitude above sea does not seem to show a correspond- 

 ing increase. The sinking is due in part, no doubt, or perhaps entirely, to 

 the compacting of the sediment. Whatever its exact nature, the facts 

 that the subsidence is greatest where the Delta is growing most rapidly, 

 and that because of the very watery condition of the material it is 

 presumably becoming more compact, make it seem probable that the 

 process is only in part, if at all, one of isostatic adjustment. 



The hypothesis better favored by the data now in hand than any 

 other, is that the mud lumps are produced by a gentle seaward flow of 



