706 GEOLOGY. 



very common tribe in our swamps and ditches, whose geographical range extends from 

 the polar circle to the torrid zone. But the difference between 

 the living and the extinct families is immense as to dimensions. 

 The horse-tails are elegant, slender, weak-stemmed plants, not 

 exceeding in tropical regions the height of five feet, and the 

 diameter of an inch, while some of the Calamites attained a 

 height of from thirty to forty feet, and a diameter of from 

 one to three feet. The figure exhibits the fragment of a Cala- 

 mite. 



Calamites caimajformis. Coniferse. Cone-bearing trees, as the fir, larch, and Arau- 



caria, or Norfolk Island pine, constitute a large and important part of the existing vege- 

 tation of all climates, and they occur in rocks of all ages from the carboniferous system 

 to the superficial accumulations. Mr. Witham has figured the trunk of an Araucaria, 

 large and branchless, found in Cragleith quarry, near Edinburgh, in strata belonging 

 to the coal-field of Mid Lothian. It was forty-seven feet long, the greatest diameter 



Trees in Craigleith Quarry. 



being five feet, the smallest nineteen inches. The trunk was very much flattened in 

 some parts, lying under 136 feet of strata, in an inclined position, as represented in 

 the sketch. The bark was converted into coal, but internally the woody texture of the 

 tree was in many places perfectly preserved. Araucarias have been alone found fossil in 

 Great Britain ; but genuine pines occur in the coal formations of Nova Scotia and New 

 Holland. 



Such are some of the vegetable forms extant in the coal measures, the greater propor- 

 tion of which are ferns ; but, from a celebrated experiment of Dr. Lindley, it appears 

 that the preserved specimens of plants are no index to the entire constitution of the 

 carbonaceous matter, or to the whole flora of the globe at the carboniferous era. He 

 immersed in a tank of fresh water.177 species of living plants for more than two years, 

 and arrived at the following conclusions : 1. That the leaves and bark of most dicoty- 

 ledonous plants are wholly decomposed in two years ; and that of those that do resist it, 

 the greater part are Coniferae and Cycadese. 2. That monocotyledons are more capable of 

 resisting the action of water, particularly Palms and Scitamineous plants, but that grasses 

 and sedges perish. 3. That Fungi, Mosses, and all the lowest forms of vegetation, dis- 

 appear. 4. That Ferns have a great power of resisting water, if in a green state ; not 

 one of those submitted to the experiment having disappeared, but that their fructification 

 perished. Thus those plants (the ferns) were found, by this experiment, most enduring 



