Mesozoic and Caawzoic Geology and Palcuontology. 19 



ness of the rock. The red sundstone has an average dip along the 

 Delaware river, of at least 10 degrees, for 30 miles. This would give 

 a thickness of 27,000 feet for this formation, or more than five miles. 

 If the mode of computation is accepted, the result must be received as 

 correct. Those who think the strata were once horizontal, and that 

 the,v have been thiown into their present inclined position at some la- 

 ter period, adopt this conclusion without hesitation. Others who think 

 the strata were deposited on a slope as we now find them, do not con- 

 sider the above to be the true thickness. They suppose that the strata 

 along the southeast border were first deposited on this northwest slope; 

 and then that the upper edges were worn off, and the material carried 

 farther northwest to be again deposited, and form new strata upon the 

 lower parts of those already deposited. Without any addition of ma- 

 terial there would in this way be a multiplication of strata, all having 

 the same dip. And such a process could go on until the formation 

 had widened out to its present extent. 



The aqueous rocks of the new red sandstone period, in Nova Scotia 

 and Prince Edward Island,* are principally coarse and soft red sand- 

 stones, with a calcareous cement, which causes them to efi"ervesce 

 with acids, and contributes to the fertility of the soils formed from 

 them. In the low part of the formation, there are conglomerates made 

 up of well-worn pebbles of the harder and older rocks. 



The volcanic rocks of this period are of that character known 

 to geologists as trap, and are quite analogous to the products 

 of modern volcanoes; and, like them, consist principally of Augite, 

 a dark green or blackish mineral, composed of silica, lime and 

 magnesia, with iron as a coloring material. Various kinds of trap are 

 distinguished, corresponding to the varieties of modern lavas. Crys- 

 talline or basaltic trap is a black or dark green rock, of a fine crystal- 

 line texture, and having on the large scale a strong tendency, to as- 

 sume a rude columnar or basaltic structure. Amygdaloid or almond- 

 cake trap is full of round or oval cavities or air bubbles, filled with 

 light colored minerals introduced by water after the formation of the 

 rock. This represents the vesicular or porous lava which forms the 

 upper surface of lava currents, just as the basalt trap represents the 

 basaltiform lava which appears in their lower and more central parts. 

 The oul}' diflTerence is, that in the amygdaloid the cavities are filled 

 up, while in the modern lavas they are empty. In some old lavas, 

 however, the cavities are already wholly or partially filled. A third 



* Acadian Geology, 1868. 



