134 THE MICROSCOPE. 



the hill; and arriving at the road, turn to the left, descend 

 the hill, and cross a sort of bridge over a somewhat insig- 

 nificant stream. Continue along the main-road a little 

 farther, to a point where it begins to ascend again, and 

 diverges to the left towards the railway; here quit it, 

 taking your course along an obscure road, nearly in a 

 direct line with the main one ; passing a windmill on the 

 right hand, and continuing until you arrive at another 

 still more obscure road, turning off to the right ; which 

 road appears as if made of the mud dredged from the 

 bottom of the river, and partially hardened. This is 

 Swanscombe Salt-marsh; and the road just described 

 leads towards Broad Ness Beacon. On either side is a 

 sort of ditch; one containing salt or very brackish water, 

 the other filled with a sort of black mud, about the con- 

 sistence of cream, the surface being in parts of a slaty 

 grey, with little patches here and there of a most brilliant 

 brown colour, glistening in the sunshine, and presenting a 

 striking contrast to the sombre shade. By carefully in- 

 sinuating the end of one of the slips of glass under this 

 brilliant brown substance, and raising it gently, it can be 

 examined with the Coddington; and it will probably be 

 found to consist of myriads of specimens of Pleurosigma 

 (navicula of Ehrenberg) angulatum, or balticum, or some 

 other species of this genus. The iron spoon is now useful, 

 as by its aid the brown stratum, with little or no mud, can 

 be skimmed off and bottled for future examination. On 

 the surface of the water in the other ditch may be noticed 

 a floating mass of a dark olive colour, which to the touch 

 feels not unlike a lump of the curd of milk, and consists 

 of Cyclotella menighiniana, and a surirella or two em- 

 bedded in a mass of Spirulina hutchinsia; and another 

 mass of floating weed, which feels harsh to the touch, pro- 

 ceeding from a quantity of a synedra, closely investing a 

 filamentous alga; and elsewhere Melosira nummuloides 

 (gallionella of Ehrenberg). 



" In a trench by the sea-wall, as it is termed, is a mass 

 of brown matter of a shade somewhat different to any 

 hitherto observed, adhering to some of the parts of the 

 trench, being partially submerged, and having a some- 

 what tremulous motion on agitating the water. This is a 



