146 MR CUNNINGHAM ON THE GEOGNOSY OF 



ciated with this sandstone, sandstone-flag is to be observed 

 they alternate and pass into each other by distinct gra- 

 dations, containing in several places very imperfect vege- 

 table relics, with layers of carbonaceous matter. The only 

 circumstance which renders the sandstone of Eigg inte- 

 resting to the geologist is, in its exhibiting a most remark- 

 able and striking instance of the. globular concretionary 

 arrangement, a kind of structure first observed in the 

 same sandstone in the Island of Skye, and afterwards in 

 coal-sandstone in Dumfriesshire, by Professor Jameson. 

 In diameter, the concretions of sandstone vary from 3 

 or 4 inches to 3 or 4 feet ; and though, in general they 

 are globular, in a few instances they become elliptical ; 



If we consider quartz in regard to the abundance of its distribution 

 over the globe in strata of an older date than coal or oolite, it will per- 

 haps be found, that there are no deposits of an extent so great as to 

 justify us in believing, that from them the secondary white sandstones 

 were derived ; and farther, the question as to where is the original for- 

 mation of quartz, is rendered still more obscure, from finding that the 

 oldest stratified quartz-rocks evince, by various characters, both struc- 

 tural and geognostical, that they have been formed from still more 

 ancient quartz. In regard to these, however, and we refer especially 

 to the quartz associated with mica and clay slates, it will invariably 

 be seen, that, if rounded masses of quartz are imbedded in a base of 

 smaller fragments, these consist of perfectly massive quartz, and ex- 

 hibit a structure having the aspect of an immediate resultant from a 

 state of fluidity. No deposits of massive quartz, however, exist, of an 

 extent sufficient to render it likely, that from them the quartz which 

 enters into the transition quartz strata, or the greywacke and the se- 

 condary sandstones, has been derived. As beds and veins in the older 

 strata it does occur ; but these are far too insignificant ever to allow us 

 to imagine that they have, in any considerable degree, contributed to 

 the formation of the strata we have mentioned. This is not a proper 

 place to enter into any details connected with the question, from what 

 formations have the derivative rocks been derived ? It is one, how- 

 ever, of difficulty, and deserving the attention of geologists, and may, 

 perhaps, lead some to believe, that whole formations have disappeared, 

 whose original existence can only be inferred from finding their relics 

 entering into the composition of newer deposits. 



