CLYPEASTER. 



[ 185 ] 



COAL. 



Ann. N. H. 3 ser. i. 419 ; Pritchard, Infus. 

 74(3; Rabenliorst, i^/or. Ahj. hi. 123 ; Wills, 

 Jn. Mic. Soc. 1880, iii. 84-j. 



CLYPEAS'TER, Lamk.— A genus of 

 Echinodevmata. 



The hairs or spines springing from the 

 shell are beautiful microscopic objects. 



CLY'TIA, Lam. — A genus of Hydroid 

 Polypes, fam. Campauulariidae. 



1 Brit, species : C. Johnstoni-=- Campann- 

 laria roluhUis. 



BiBL. Ilincks, Hyd. Zooph. p. 140. 



CNEMLDA'KIA, Presl.— A genus of 

 Cyathese (Polypodiaceous Ferns). Now 

 consolidated with Hemitelia, 



Fig. 129. 



Fig. 130. 



Fig. 131. 



Fig. 132. 



C. (Hemitelia) horrida. 



rig. 129. Fragment of a pinnule, the sori covered by 

 indusia. Magnified 5 diameters. 



Fig. 130. A sorus with indusium destroyed. 



Fig. 1-31. The same, side view, showing the fragment 

 of the indusium at the base. 



Fig. 132. Vertical section of a sorus. 



Figs. 130-132 magnified 25 diameters. 



COAL. — This substance, although classed 

 from its mode of occurrence in nature in the 

 mineral kingdom, is in all cases of vegetable 

 origin. The degree, however, in which 

 traces of organic structure may be detected 

 in it varies extremely. Coal may be either 

 tolerably irure, containing but shght admix- 

 ture of earthy matters, or it may contain 

 large quantities of earthy substance, and 

 pass gradually into a carbonaceous impreg- 

 nation of an earthy basis, as in the various 

 modifications of bituminous shales. In the 



next place the degree of metamorphosis of 

 the vegetable matter may be equally varied, 

 so that we have it .still retaining its struc- 

 ture very evidently, as in liynites, «fcc., or 

 with the structure greatly destroyed, or 

 altogether lost, as in much ordinary coal and 

 anthracite, which however are apparently 

 of somewhat ditl'erent origin from the more 

 recent lignites. Some of the old coal-beds 

 appear to have been formed from depo.^its 

 analogous to our peat-bogs, and hence na- 

 turally consist in great part of vegetables 

 whose remains soon become imdistingiii,<h- 

 able; but that arborescent vegetation was 

 also prtsentand contributed to form the coal, 

 is proved by the detectic >n of woody .struc ture 

 somewhat like that of the Coniferse in certain 

 specimens of coal. Sometimes the woody 

 structure is even evident to the naked eye, 

 in a charcoal-like appearance of the frac- 

 tured surface or bed-planes of coal. In many 

 lignites the coal consists of trunks of trees 

 converted into coal without much alteration 

 of the appearance of texture of the wood ; 

 and in these the structure is very readily 

 made out by means of the microscope. 

 Some old coal is largely or entirely compo.'^ed 

 of sporangia of Lycopodiaceous or Lepido- 

 dendroid plants, cemented together by a 

 brown substance derived from the decom- 

 position of the tissues of the coal-formino- 

 plants. It would be out of place here to 

 enter upon the geological and chemical 

 questions connected with coal; the object 

 of applying the microscope to it is to ascer- 

 tain the existence or absence of organic 

 structure. For this purpose various methods 

 are employed. That most in use is the 

 preparation of exceedingly thin slices in the 

 manner usually adopted for fossil structures, 

 but the brittle and opaque character of 

 coal opposes great difficulties here. Traces 

 of structure may be made out in some 

 cases by grinding coal to fine powder and 

 examining the fragments ; but this plan is 

 very uusatisfactoiy. A third method is to 

 burn the coal to a white ash, and examine 

 this under the microscope : it often exhibits 

 perfect skeletons of vegetable cells, but the.^e 

 are very fragile, and require great care in 

 their management. By imbuing them very 

 cautiously with turpentine and Canada bal- 

 sam, and placing on the covering glass when 

 the latter has become rather firm, permanent 

 preparations may often be obtained. Schulze 

 recommends boiling in nitric acid before 

 incinerating the coal. Tlie method which 

 has been attended with most success in our 



