GEOLOGICAL REMARKS. 



431 



sufficient to prevent the due aeration of the inner cellules, without 

 direct communication with the atmosphere. Vide Musci ! ! Hence 

 the inner tubes of the leaves of the generality of aquatic plants, 

 (exception Eriocaulon fluitans.) 



What is the cause of the plurality of radicles in certain species 

 of Lemna, and their blank in others ? It will be necessary on this 

 point to examine well the sheaths of Azolla, and to look at the Mergui 

 ^Eschynanthus. 



The formation of Affghanistan is very curious : it consists of a wide 

 extent of country, variously elevated steppes being separated by ridges 

 usually very accessible, generally isolated. The mountainous part 

 varies as to its formation, but there is no variety in the declivities 

 and acclivities forming the lower elevations, which are composed of 

 conglomerate ; nor is there much in the usually narrow strip at the 

 lowest portion of each steppe or valley, which is very generally the 

 only cultivatable portion. 



In the Khyber ghat the ridges are either of limestone or slaty 

 rocks, between which conglomerate occurs of various thicknesses ; this 

 being dependent on the angle of the mountains forming the sides of 

 the ghat : it is from this conglomerate in such places consisting 

 usually of a loose texture that the very excellent roads (for moun- 

 tainous passes) are naturally made by the draining streams, which are 

 only periodical. The conglomerate consists of water- worn stones of 

 all sizes, even boulders are not unfrequent, yet the wearing is such as 

 occurs in courses now filling the beds of torrents. The conglomerate 

 increases in density and adhesion towards Lalpoor, and in many 

 places is exceedingly hard. 



Whatever the country may have been previously, one might ex- 

 plain its present appearance by supposing it to have consisted of a 

 tolerably level extent of conglomerate, with here and there a strip of 

 soil in the lowest part of each portion, and that the elevation of 

 the mountain ridges was of subsequent occurrence : this would 

 account for the formation of the lower slopes, and the frequent isolation 

 of small eminences of the same character as the neighbouring moun- 

 tains. It will account for the appearance of the conglomerate in 

 every ravine until the top of the culminating point is reached. 



As the mountains were elevated, portions of conglomerate would 

 be detached, and these resting again on all suitable places, would 

 account for the existence of conglomerate on certain parts which are 

 flatter than usual. 



