886 



PRINCIPLES OF STRATIGRAPHY 



ejected from them shot in some cases 20 feet into the air. Many of 

 the craterlets, especially those formed during the Calabrian earth- 

 quake, are merely funnel-shaped holes in the ground, and so re- 

 semble the volcanic explosion craters. (Fig. 242.) Such crateilets 

 formed in the Mississippi A^alley during the earthquake of 181 1. 

 They were commonly surrounded by a ring of sand and carbonized 

 wood, sometimes as much as 7 feet in height. They have a diam- 

 eter ranging from 20 to 100 feet, and some were sounded to a depth 

 of 20 feet or over. 



Much sand and water is ejected from these and is spread 

 over the surrounding country, which may thus be blanketed by a 



Fig. 242. Funnel-shaped holes formed during the Calabrian earthquake of 

 1783. (C. Vogt.) 



layer of sand brought from below, the analogue of a lava 

 flow. Sulphuretted hydrogen frequently accompanies these erup- 

 tions. 



Fossil examples. Ancient craterlets of the type above described 

 have been noted in some cases. Thus, on the coast of East Angle- 

 sey, in Wales, sandstone pipes have been observed, penetrating the 

 Ordovicic limestones, and having a general funnel form comparable 

 to the funnels formed by the Calabrian eartliquake. They are 

 continuous above with a spreading blanket of sandstone, which 

 may be the ejected layer of sand. The entire series is again cov- 

 ered by the Ordovicic limestones of the region. A section of this, 

 copied from Hobbs, is shown in Fig. 241. Care must, however, be 

 exercised to distinguish these fissures from the solution fissures 

 subsequently filled by sand and forming the organ-pipe structure 

 described in a preceding chapter. 



