246 Hbbbs — Features Formed at the Time of Earthquakes. 



whatever district and adopt for all the same explanation. 

 Amid all the variety of ingenious theory, it is a little surpris- 

 ing that of those who have addressed themselves especialty to 

 the problem, one only has given weight to a possible birth of 

 the mounds at the time of earthquakes in the district. Mr. 

 A. C. Teatch, the best recent authority upon the geology of 

 the district, has considered the possibility of this origin for 

 certain of the mounds, but believes the dune and ant-hill 

 theories the best supported. Shepard has, however, been able 

 to show conclusively that the low mounds of the " sunk 

 country " are " sand blows " — mounds three or four feet in 

 height with diameters of 20 to 100 feet, frequently slightly 

 hollowed at the center — mounds which came into existence 

 during the earthquake at New Madrid in 1811-12. 



Veatch has concisely stated the general characteristics of the 

 so-called "natural mounds" of the Gulf Plain in the following- 

 words, the italics being the present author's :* 



"They (the mounds — eel.) occur irregularly throughout the 

 coastal plain in northern Louisiana, northeastern Texas, Arkansas, 

 and southeastern Missouri, except in the present flood plains. 

 They are best developed on the Port Hudson terraces, but extend 

 also over the hill lands. They are not restricted to any geologic 

 formation or any range of elevation. The material of which 

 they are composed is commonly a very fine loam, which is reported 

 by the agriculturists to be coarser and quite distinct from the sur- 

 rounding soil, which is commonly clay. Oil-ivell drillers in 

 southern Louisiana and southeastern Texas report the material 

 in these mounds to be entirely different from the surrounding soil 

 and exactly the same as the fine sand found beneath the 50 to 100 

 feet of surface clay. The apparent difference in composition is, 

 however, not so great as it seems at first sight and is in part due 

 to the greater elevation and consequent better drainage of the 

 mounds. Careful mechanical analysis will be necessary to deter- 

 mine the true character and degree of this difference." 



Udclen has shown* that of 59 mounds near Olivia, Texas, 

 the greater number are less than 30 feet in diameter and 7 

 inches in height, and, further, that it is the larger mounds 

 which show the distinct pittings at the center. 



The object of the present article is to draw attention to the 

 fact that the region in question is one of notable seismicity, 

 and to point out that sand and water fountains, as well as mud 

 volcanoes, with their products, " sand " or " mud " cones and 

 " craterlets," are almost universally produced in connection 

 with great earthquakes. The derangement of the ground 



* Professional Paper, U. S. Geological Survey. No. 46. p. 155. 

 f Science. Jtine 1, 1906, p. 850. 



