446 TRANSACTIONS OF TPIE AMERICAN INSTITUTE. 



Dr. Stevens commenced liis lecture on American Geology, by 

 exhibiting a map of the North American Continent, as he sup- 

 posed it to have existed in the carboniferous era ; showing, at 

 that time, the Gulf of Mexico, as it is now called, extending up 

 the Mississippi valley, and across the United States into the 

 British possessions. The North river was, also, at that time, in 

 his opinion, an arm of the sea, extending to the St. Lawrence, 

 and separating New England from the rest of the continent. 

 Only three orders of plants were then in existence, as far as 

 known. These were : 



First, Fucoids, or sea plants. 



Second, Land plants, endogenous. 



Third, Land plants, exogenous. 



The fish exhibited is of the family of sword fishes. The 

 organs, which resemble" teeth, were not actually teeth, but an- 

 armature, on the outside of the jaw. The head was composed of 

 solid plates. The eyes were very large, looking upwards as well 

 as outwards.. The scales were of solid bone, and the tail was 

 heterocercal. This was, as far as known, one of the first class of 

 fish created. The Garpike of Lake Erie, and a similar fish in 

 the Earitan, are the only representatives of this class now re- 

 maining in American waters. It is allied to reptiles, and had 

 many of the instincts of reptiles. Paleontologists would say 

 that it was an indication that by and by reptiles were to be 

 created. The scales of the garpike are so hard when dry that 

 they will strike fire like flint. 



The peculiar iron ore of this age is a carbonate of iron. In 

 earlier formations iron is always in the condition of an oxide, 

 and often magnetic, but no magnetic iron ores are ever found in 

 the coal region. Nor are Galena, copper, silver, gold, or zinc 

 found in the true coal strata. It seems as if no metal could be 

 found in the formations of this age when carbonic acid gas was 

 in such preponderance, unless it would readily combine with car- 

 bon ; and iron is the only onfc that will. 



A STEAM GUNBOAT. 



Mr. Johnson exhibited a drawing of a gunboat with the 

 important works below the water line, in accordance with Mr. 

 Fisher's suggestion of last week. The draft is obtained by a 

 horizontal smoke pipe, thereby relieving the gun deck. As a 



