THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE V. VOL. X. 



No. VIIL— AUGUST, 1913. 



OlilG-insr^^JL. .A.K,TIOI-.ES- 



I. — Note on a Process of FossiLizATioisr in the Paleozoic 

 Ltcopods.^ 



By E. M. Kindle, Department of Mines, Geological Survey of Canada, Ottawa, 



Ontario. 



(PLATE XI.) 



MOST collections of fossil plants include specimens of tree-trunks 

 or branches in which the bark is preserved in great perfection, 

 while no trace of the structure of the trunk within the bark remains. 

 Striking examples of this type of fossilization, in which the bark is 

 preserved in exquisite detail while the space within the bark is 

 wholly filled with fine siliceous sediments showing no trace of the 

 original plant structure, occur frequently among the various species 

 of Sigillaria and Lepidodendron. The fossilized ai'mour-like outer 

 cortex of Lepidodendron fails to retain any remnant of the inner 

 woody material about as often as the various molluscan species of 

 Spirifer fail to preserve their delicate internal spires. We know 

 from the silicified specimens which have been found that the greater 

 part of the trunk in Lepidodendron is occupied by a soft middle cortex 

 which is very readily disposed of by micro-organisms. The relatively 

 small cylinder of secondary wood which is found in most species 

 which have attained to a large growth was itself rather susceptible 

 to decay, the tracheids being relatively thin-walled, with the medullary 

 cells very large and the rays voluminous.^ Innumerable examples of 

 the entire failure of the woody tissue of these Lycopods to survive the 

 processes which left the outer cortex admirably preserved occur in the 

 fine-grained sandstones of Pottsville: age in Orange County, Indiana. 

 These beds, which have long been quarried for the manufacture 

 of whetstones, contain numerous fossil trunks of Lepidodendron 

 veltheimianum, Sternb. (Plate XI), which show the carbonized bark in 

 a good state of preservation, while the space inside the bark is wholly 

 filled with very fine sand similar to that of the strata in which the 

 fossils lie. These sand-filled tree-trunks generally retain approximately 

 their original outline, except for a slight flattening of the trunk. 

 Two trunks of Lepidodendron about 10 inches in diameter and 8 feet 

 in height were observed at the time of my visit standing upright in 

 one of the whetstone (]uarries. The largest trunk seen had a circum- 

 ference of 4 ft. 8 in. The usual size of the trunk is 6 to 15 inches iti 



^ Published with the permission of the Director of the Geological Survey 

 of Canada. 



* Letter to the author from David White. 



DECADE V. — VOL. X. — NO. VIII. 22 



