492 NOTE ON THE ORIGIN OF " KEROSENE SHALE," 



margins of the depression, and also on the sides of island-like 

 elevations which are scattered about it." On page 104 {loc. cit.) 

 he states, " Another writer in the Register (May 8th, 1866) 

 describes thin sections as 'exhibiting under the microscope, 

 especially if moistened with a solution of caustic potash or 

 benzole, a granular and cellular structure with entangled fibres 

 resembling the fibres of decayed fungi.' Mr. Berkeley has 

 also, as he informs me, been struck with this pseudo-cellular 

 structure. Mr. Archer, the Secretary of the Dublin Micro- 

 scopical Club, to whom I submitted a fragment for examina- 

 tion, gives, I think, the true explanation of this appearance. 

 He writes to me in a recent letter to the following effect : — 

 * I think the substance in question is certainly organic — some 

 kind of gum with accidental things imbedded, such as bits 

 of vegetable tissue, some confervoid or fungal threads, and the 

 like. Once I saw a Cymhella in the material, but I never could 

 find the same place again. The matrix appears to possess a 

 certain amount of quasi cellular appearance by reason of streaks 

 running here and there in a quasi reticulated manner. Of course, 

 in the act of making the section, the knife leaves a number of 

 superficial streaks which one must throw overboard.' The struc- 

 ture of the matrix noticed above may doubtless be attributed 

 to a physical fibrillation due to the mere shrinking and hardening 

 of the substance. That it must have been in a soft, if not fluid 

 state, is evident from the miscellaneous collection of crypto- 

 gamic reliquice which different microscopists have detected in it. 

 Their miscellaneous character is a sufiicient proof that their 

 presence is adventitious. As to the origin of the substance, 

 opinions are the most discordant possible. The suggestion which 

 occurred to Mr. Berkeley that it is the residue of some crypto- 

 gamic plant, is, at first sight, very plausible. One can imagine 

 such a residue being formed by Bromicolla aleutica, which forms 

 in the Aleutian Isles a layer two feet thick of a Nostoc-like sub- 

 stance, covered with a gramineous vegetation. One can imagine 

 it also to result from the drying up of a lake covered with 

 Hoomo7iema fluitanSj the ' vegetable turtle-fat,' described by 



