jgi8.1 ON THE FORMA'nON OF ROCKS. 29r 



the rocks generally found accompanying the gray- 

 wacke shist ; and tliough it is like the red sandstone, 

 and has some resemhlance to the formation of gray- 

 wacke shist, yet the difference both in structure and 

 position must perhaps exclude it from those forma- 

 tions. 



Transition J^eptunian Rocks, 



The character which distinguishes this from tlie 

 secondary, may perhaps be the nature and arrange- 

 ment of the cements ; in the aggregates of the seconda- 

 ry this cement is produced by infiltration ; the round- 

 ed particles generally touch each other, but in the 

 transition, the particles when small, appear to have 

 been swimming or floating in the cement, which seems 

 to have prevented them from touching, and usually 

 forms a more homogeneous mass. When the parti- 

 tides are large, gravitation may have overcome tlie 

 resistence of the cement, and they touch ; but even 

 then the cement occupies more of the space, than ia 

 tlie puddings of the secondary. 



The stratification of the transition rocks, seems to 

 constitute another dividing characteristick, being ge- 

 nerally at a dip from tlie horizon, and seldom or ever 

 found horizontal ; but the limits near the dividing line 

 will, perhaps, for a long time remain doubtful. 



The clay found in the sandstone of the secondary 

 is generally in a soft state, earthy in its fracture, and 

 has little or no resemblance to tlie slate, and other ar- 

 gillaceous rocks, mixed and alternating with the tran 

 sition aggregates. 



