SECONDARY ROCKS—ORGANIC REMAINS. 31 



sandstone series. The plants which do occur, though, 

 perhaps, some may be unknown in other coal-fields, present, 

 however, a general similarity to those of similar districts. 

 The Sphenopterides, the Lepidostrobi, Sigillarice, Stigma- 

 ria, Lepidodendra, and Lepidophyllites, abound in numerous 

 localities, often in a state of the greatest preservation, and 

 in others there have been found trunks of gigantic members 

 of the Pine tribe. The remains of this class, found in the 

 sandstone of Craigleith, are well known, and their structures 

 have been completely unfolded by Mr William Nicol, as 

 stated in a memoir in the Edinburgh New Philosophical 

 Journal,* the result of which is, that all belong to coniferce, 

 a series of vegetable bodies which that observer has found 

 to form, without any intermixture with dicotyledons or mo- 

 nocotyledons, all the great vegetable stems of the Indepen- 

 dent Coal Formation. Concerning the states in which 

 these fossils are found, it may be remarked that they are 

 more or less bituminated, some portions even being changed 

 into coal ; and that Professor Jameson, in his lectures, 

 states it as his opinion that the vegetable matter in these 

 fossils occurs sometimes but slightly changed, so that the 

 earthy matter may be removed by chemical agency, leaving 

 the wood but little changed as to structure and composition. 

 The fossils detected in sandstone, are most frequently 

 found in the state of sandstone, and the whole of the vegetable 

 structure having been removed, nothing remains to in- 

 dicate their nature but the external form. The causes which 

 have effected these changes are unknown, and the discovery 

 of them would in all probability explain phenomena at pre- 

 sent but imperfectly understood. If an organized body 

 imbedded in a rock of chemical origin is found to be 

 of the same composition as the stratum in which it oc- 



* Edinburgh New Philosophical Journal, vols. xxiv. p. 361 ; xxviii. 

 p. 155; xxx. pp. 137-310 ; xxxii. p. 338. 



