COLLECTING DIATOMS. 37 



localities we may expect to find some of the rarer alpine forms, Navi- 

 cula rhomboides, obtusa, Pinnularia divergens, lata, and Alpina, for 

 instance. The pale-green flocculent mass growing in quantities like a 

 conferva is well worth collecting, for it is a pure gathering of Tabellaria 

 ftocculosa and jenestrata. 



" In tramping over this quaking bog, it is well to roll up a bundle 

 of the Sphagnum, for on afterwards squeezing out the water we may be 

 rewarded by finding some of the rarer species of Pinnularia such as 

 hemiptera and Alpina. 



" Before leaving this rocky part of the country for the flat country 

 below, let us scrape some of the brown mucus from the face of the 

 dripping rocks, for it will probably yield such forms as Epithemia, 

 Cocconeis Thwaitsii, Navicula truudis, Denticula sinuata, &c. 



"The weather being warm, we will quench our thirst at the little 

 spring in the cavern-like hollow in the rocky roadside. Observe, the 

 roof of the little cavern is quite covered with a chocolate-brown mass, 

 which feels rough and gritty to the fingers. Here is a splendid and 

 pure gathering of Orthosira arenaria, and I recommend you to take a 

 good store of it away with you, for it is seldom one finds this fine 

 form so pure and unmixed. 



" Proceeding towards the low country, let us take a scrape from the 

 side of this horse-trough, for it is quite brown. It is well we have 

 done so, for it is a nice pure gathering of Cyclotella operculata and 

 Pinnularia pygmaa. 



" Passing a little further on, we come to a clump of ash trees, 

 with a crop of moss growing on their trunks. Perhaps you may smile 

 when I proceed to peel off this moss and store it away in a bundle 

 in my satchel. On washing the moss afterwards, however, I may be 

 rewarded with some of our most local and rare species, viz., Orthosira 

 mirabilis, mixed with Navicula tumida, Pinnularia borealis, and Ortho- 

 sira spinosa. 



"Having secured a bundle of moss from the tree-trunks, we will 

 take another from the roof of this old thatched cottage, the north side 

 of which is quite carpeted with beautilul green moss. This will pro- 

 bably yield Nitzschia Amphioxys and Pinnularia borealis. 



" The white-colored stratum of earth exposed in the cutting on the 

 roadside must now be examined, for it is probably a deposit of fossil 

 diatomaceous earth ; in which case a large piece must be secured. 



"These fossil deposits are generally composed of a compact mass of 

 Diatomaceae of recent as well as extinct species. The deposit we are 



