260 ANNUAL OF SCIENTIFIC DISCOVERY. 



Mr. Foster remarked, that, from the investigations of the Messrs. 

 Rogers, and others, it was indisputable that the metamorphism of the 

 rocks of the Appalachian chain took place at the close of the Carbo- 

 niferous era ; but that the sandstone of the Connecticut valley had not 

 partaken of that metamorphism. It was also highly probable that the 

 sandstone was older than the coal deposits of Richmond, which were 

 proved to belong to the Oolite. Therefore, whatever might be the 

 ultimate position assigned to this sandstone, it was intermediate be- 

 tween these two epochs. It was found, too, as a general rule, that 

 whenever a great change occurred in the physical conditions of the 

 earth, those changes were indicated by the character of the deposits. 

 Thus, the base of. many of the great systems of rocks is occupied by 

 conglomerates, succeeded by coarse sandstone grits ; and it was not 

 until after the lapse of a considerable time, that the finer silts were 

 thrown down. It was also found that these coarse grits and conglom- 

 erates were barren of types of organic life ; whereas the finer silts 

 contained the most abundant traces. The fact, therefore, that the 

 sandstone at the base of this series of rocks was unproductive in fossils, 

 while the shales contained numerous traces of their existence, did 

 not necessarily imply that the rocks belonged to two epochs of deposi- 

 tion. 



As to the unconformability of the two portions, as described by Mr. 

 "Wells, he remarked, that this sandstone, throughout its range, exhib- 

 ited numerous instances of the intrusion of trappean rocks. These 

 took place at successive intervals, as was evidenced by the manner in 

 which they were intercalated with the sandstones. These belts, like 

 those of Lake Superior, were not the result of protrusion between the 

 strata, but of overflows, like submarine volcanoes, and mingling with 

 the sediments there being accumulated. There might, therefore, be 

 an unconformability between the upper and lower portions of the 

 series, without the necessity of presupposing a great lapse of time, 

 unless that unconformability was found to prevail over an extended 

 area. 



ON THE LITIIOLOGICAL CHARACTERS OF THE SANDSTONE AND TRAP OF 



LAKE SUPERIOR. 



AT the American Association, Cincinnati, Mr. J. "W. Foster, U. S. 

 Geologist, in a description of the rocks of the Lake Superior district, 

 adverted to some curious lithological characters exhibited in the trap 

 and sandstone formations of this region : 



" The changes which have taken place in the structure and lithological 

 character of the sandstone and trap, are of an interesting character, 

 and throw much light on the mode of formation of the trappean beds. 

 The upper portions of the sheets of the bedded trap are often highly 

 vesicular, resembling pumice. Fragments of amygdaloid, sometimes 

 rounded, at others angular, are found enclosed in the pumice-like trap, 

 as though they had become detached from, and afterwards reunited to, 

 the mass while in a soft state. Numerous short and irregular fissures, 

 extending to no great depth, are observed on the upper surface of the 



