554 MINERALOGY OF THE REDttEAli* 



posed for some time to the influence of the at-* 

 mosphere, the fresh fracture presenting a homo- 

 geneous surface. These pieces, which appear at 

 first sight to be fragments, are merely contempo- 

 raneous portions of the rock ; they present no 

 rounded water-worn surface, and at one extremity, 

 at least, pass by an insensible transition into the 

 rock in which they are enveloped. The term 

 sandstone-conglomeratey ought to be restricted to 

 denominate this kind of rock, as it must either 

 mean sandstone in the form of fragments or balls, 

 or sandstone in heaps. When the term includes 

 the gravelstone of Colonel Imrie, it evidently 

 has obtained too great a latitude of signification 



In all the preceding strata of sandstone, there 

 occur beds of slate- clay, seldom above a foot in 

 thickness, and of a similar colour to the surround- 

 ing rock. The slate-clay is often in the form of 

 angular pieces included in the sandstone, in which 

 it also occurs in indistinct layers. The longitu- 

 dinal fracture is usually glimmering, the cross 

 fracture dull. It passes, on the one hand, into 



* Limestone-conglomerate, in the restricted sense of the 

 term, is a rock oi frequent occurrence. It may be observed in 

 Arthur's Seat, at Innerkip in Renfrewshire, and near the 

 Rumbling Bridge in the county of Perth. In all these situations, 

 it appears to be an inmate of the old red sandstone formation. 

 I consider Arthur's Seat as a portion of this formation. Seve- 

 ral facts in proof of this, may be found in WiLLrAMs's Mineral 

 Kingdom. / 



