CHAP. 5.] ROCK FOEMATIONS. TIPPEll JURASSIC, 51 



Prolonged but unavailing search was made over large portions of 

 the ground occupied by these rocks for even a 



Interstratification of 



terrestrial and marine fragment of one of the Palaozamim known to 

 fossil-bearing beds. 



occur in other parts of the formation; but not 



until the most westerly extension of this sub-group came under examin- 

 ation was anything of the kind observed. At one place there a few 

 fragments of Zamim and ferns were found in a thick band of shales 

 overlyingj with the intervention of several feet of these shales^ the marine 

 fossil zone of the locality ; while at some distance above^ a thick bed of 

 hard sandstone contained belemnites and obscure bivalve shells. The 

 succession and intercalation being so far perfect, but the ground so dis- 

 turbed by igneous intrusions. Sec., that the separate beds could not be fol- 

 lowed out for any great distance. 



Upper Jurassic. 



Above the group so far described the sandstones become more 



brown in color, speckled with distinct white quartz 

 Transition beds. 



grains, thick, with red ferruginous nodules, or 



more frequently thin and flaggy, rapidly alternating with shaly layers 

 and partings. Red colors begin to predominate, and pale gray shales 

 are found which contain but rarely a few Zamice ; coarse grits and con- 

 glomerates, more rarely seen below, may be met with, and occasional 

 thick bands of gray tough shale, full of plant fragments as usual, but 

 seldom of recognisable form. These beds have often considerable thick- 

 nesss, preading over wide sjiaces, and the indefinite boundary between the 

 lower and upper groups may be drawn almost anywhere through them. 

 Succeeding these are the more characteristic upper beds consisting 

 of coarse white sandstones, some formed of large 



Upper Jurassics. 



grains of white quartz loosely held together by a 

 felspathic base, many gravelly and conglomeratic beds, interlamiuations 

 of coarser sandy and more argillaceous layers with crisp biscuit-like 



( -51 ) 



