STEPHENSON: TONGUE, A NEW TERM 243 



aa pedestal sloping outward steeply, scored vertically in places, 

 9 metres high above lake level, and showing a rough scaly ap- 

 pearance of greenish black color. At lake level its diameter 

 was approximately 45 metres. 



The flat islet from which this mass was raised was first noticed 

 February 8, 1917, after 9 metres of subsidence of the lake from 

 its highest level of February 1. The island then appeared as 

 a shoal 60 metres out from the shore in the northern part of 

 the lake, and was supposed to be the product of collapse of a 

 shore point of the eastern bench, which had in turn emerged 

 first as an islet in November, 1916. The locus of the final tab- 

 ular mass was farther south than either of these. 



There is little to be said at this time about the lithology of 

 the aa. It is a heavy block lava which consists of the usual 

 complete, scoriaceous, vesicular units in the talus 5 to 30 cm. in 

 diameter, showing no fracture surfaces, and of reddish or green- 

 ish brown color. In the wall the rock is in places grooved ver- 

 tically like scraped wax, a steel-grey rough substance, and over- 

 hanging drip bodies are hard, scoriaceous and quite like the 

 block units. The material is nowhere ropy or membranous like 

 pahoehoe, and has not the slightest resemblance to the crusts 

 and overflows of the lake. It is very similar to the aa flow which 

 was ejected from Mauna Loa in 1916. 3 



STRATIGRAPHY. — Tongue, a new stratigraphic term, with 

 illustrations from the Mississippi Cretaceous. ] Lloyd Wil- 

 liam Stephenson, Geological Survey. 



The stratigrapher is at times confronted with the problem of 

 adequately treating certain tongue-like extensions of one for- 

 mation into contemporaneous deposits of different lithologic 

 character and belonging to another formation. 



A simple hypothetical case is diagrammatically shown in 

 figure 1. 



3 Amer. Journ. Sci., March, 1917. 



1 Published with the permission of the Director of the United States Geologi- 

 cal Survey, and of the Director of the Mississippi State Geological Survey. 



