GEOLOGICAL PAPERS. 107 



It is believed by the writer that the Sweetland Creek shale is a 

 western extension of the "Black shale" in Ohio and that it is 

 identical with the Devonian shale at Milwaukee. From these 

 scattered wells, in which it has been identified by the examination 

 of drill cuttings, it seems likely to be continuous under the Miss- 

 issippian in the central part of the state, and it was once probably 

 a continuous deposit, laid down in a sea extending from Ohio to 

 Iowa. Its uniform development and its limited thickness indicate, 

 as Professor Dana has stated, nearly uniform conditions of level 

 over a great extent of the surface of the interior of this continent. 



AN AMERICAN LEPIDOSTROBUS. 



By John M. Coulter axd \V. J. G. Land, 



University of Chicago, 



(Abstract.) 



Our knowledge of the structure of coal measure plants has been 

 derived chiefly from English and French material in which the 

 structure has been preserved, American coal measure plants hav- 

 ing been found only as impressions or casts. Recently there came 

 into our possession a specimen of Lcpidostrohus (the strobilus of 

 Lepidodcndron) from a coal pocket in Warren County, Iowa, 

 whose structure is admirably preserved. The specimen is not a 

 complete strobilus, the lower portion being missing, so that all 

 evidence as to the heterosporous condition is gone. 



Sections were made of the strobilus. and a complete description 

 of its structure became possible, even many of the spores (pre- 

 sumably microspores) being well preserv-ed. The general struc- 

 ture of Lepidostrobus is well known from foreign material, the 

 most characteristic feature being the radially elongated sporan- 

 gium, which extends along the whole adaxial face of the stalk of 

 the sporophyll. A curious method of dehiscence was discovered, 

 the sporangium opening by a longitudinal slit along the median 

 line for a httle more than half its length from the base, and then 

 the slit forks and is represented in the distal half of the sporan- 

 gium by two diverging slits, which leaves between them a large 

 triangular flap of the sporangium wall. 



The strobilus was evidently a mature one which had fallen and 

 remained in water or moist soil, for rootlets had penetrated 

 between the sporophyll here and there, and the rootlets in turn 



