Hobbs — Features Formed at the Time of Earthquakes. 249 



ants of the district claim that the better quality of water is 

 found by boring in the mounds of the valley. In the words of 

 Shepard :* 



"Further, we find today that large volumes of water are con- 

 stantly coming to the surface as springs in this district ; that 

 these springs are numerous along the lines of fissure : that deep 

 artesian wells around this region bring up this same variety of 

 sand with lignite, some, as at Memphis, when first sunk, ejecting 

 large chunks of the lignite ; that the sand and lignite brought up 

 in the deep wells are similar to the same substances brought up 

 by the innumerable springs that feed the lakes and streams of this 

 district, and that they are apparently the same as that which sur- 

 rounds the blow holes and fault scraps, and which covers, as 

 with a vast sheet, the considerable areas in the sunken district." 



The association of oil with the mounds of_ the Gulf Plain is 

 further of interest, and especially because it is the low mounds 

 of the spindle-top type in which the petroleum is found. Fen- 

 n em an states that the chance of finding oil under the elevated 

 spots in the plain is vastly greater than elsewhere. He fur- 

 ther says :f 



" There is some reason for thinking that such structures are 

 ranged along lines of slight crustal deformation or disturbance. 

 If such lines exist they probably trend northeast and southwest. 

 This probability mav well be recognized in prospecting for new 

 fields." 



The northeast-southwest direction is the one which, accord- 

 ing to Lyell, was by far the most common direction of the fis- 

 sures produced at the time of the New Madrid earthquake. In 

 view of the vast deposits of sulphur which, have been found 

 to underlie portions of the Gulf Plain, it is worthy of men- 

 tion that the earthquake of New Madrid was possibly 

 unique in the respect that the shocks were accompanied by 

 emissions of sulphurous vapors (probably sulphureted hydro- 

 gen) causing great discomfort and rendering the river water for 

 days unfit for drinking purposes. 



Sand blows, mud volcanoes, craterlets, etc. are clearly 

 closely related phenomena and are to be ascribed to the verti- 

 cal movement of water, gas, sand, etc. along the widened por- 

 tions of earth fissures. Their connection with larger tectonic 

 movements as the resulting derangement of the ground water 

 system, is only beginning to be appreciated. Perhaps the most 

 striking and significant single characteristic of the mounds 



*L. o., p. 58. fL. c.,p. 124. 



