200 NERBUDDA DISTRICT. 



These deposits are -therefore commonly found resting on one layer of 

 trap, and covered by another : and hence the name first given to them 

 by Dr. Carter of Bombay, of the " Intertrappean Lacustrine For- 

 mation" (a) was derived. 



The term has since been used with greater latitude and made to imply 

 geological age as well as stratigraphical position, being often applied to 

 beds which neither rest on, nor are covered by trap, provided that 

 there be evidence to lead to the belief that they belong to the same 

 age as those other beds which are literally intertrappean. 



The " intertrappean " deposits as thus defined have long been known to 

 geologists, and much labor has been devoted to the collection and to the 

 study of the fossils with which they abound (see Introduction to this 

 paper where reference is made to some of those researches.) The fossil 

 evidence will not, however, occupy us at present ; and our remarks will 

 be confined to a consideration of the lithological character and position 

 of the beds. 



So far then as we have to do with them, the beds of this intertrappean 

 age are the remains of lacustrine deposits, former- 

 ly accumulated in probably detached basins, and 

 under conditions slightly differing in different places. 



This variety in the circumstances under which the beds were found is 

 proved by the varied lithological characters which they now present. 



Most of these, as would naturally be supposed from their mode of oc- 



, ... currence, have been much baked by the super-in- 



Indurated siliceous va- * J r 



riety. cumbent basalt, and they very commonly occur 



as a flinty or porcelain-like rock, with a conchoidal fracture, and of a 

 dark blue grey, or sometimes a yellow brown color. Beds, and patches of 

 beds, presenting these characters are found almost every where within 

 the trap area, and they frequently contain great numbers of shells and 

 many fragments of silicified wood. 



(a) Journal, Bombay Asiatic Soc : Vol. V. p. 267, 1854. 



