THE GEOLOGIST'S TKAYELING HAND-BOOK. 



2-15. PALEOZOIC. 



2-4. CAMBRIAN (OR LOWER SILURIAN) AGE. 



2 a. Acadian. This series is found at Braintree, in Massachusetts, at St. 

 John, in New Brunswick, and at St. John, in Newfoundland. It includes one 

 thousand feet or more of fossiliferous sandstone and shale, and according to Dr. 

 Hunt, corresponds to the Menevian of Great Britain. It has only been found 

 along the north-eastern border of the Atlantic belt. It is remarkable as a f ofesil- 

 if erous rock below the Potsdam, which had, before its discovery, always been con- 

 sidered as the lowest formation of that description on the continent. 



2 b. Potsdam. The Potsdam sandstone, was for a long time considered as 

 the lowest sedimentary fossiliferous rock. It is usually of a purely quartzose 

 character, generally gray, though often striped, and sometimes partially or 

 entirely red. In places it appears as a conglomerate, but sometimes the enclosed 

 masses are angular, showing them to be near their source. Hall, N. Y. R, 27. 

 It is a hard silicious sandstone, white, red, gray, yellowish, and frequently striped. 

 Some strata of this rock are covered with the most beautifully characterized 

 ripple-marks as perfect as if just formed on the sand of a sea-beach, while 

 the rock is the most indurated kind of sandstone. Its lower portion is a 

 granitic conglomerate, in which large masses of quartz, the size of a peck 

 measure, are often enveloped ; they are rounded and water-worn, and held together 

 by a finer variety of the same material. On the Canada slope, where the 

 mass is 300 feet thick, it is wholly a conglomerate, made up of coarse materials. 

 The part which is properly a sandstone, has two principal varieties, a close grained, 

 sharp edged mass, with natural joints traversing it in two directions, but so closely 

 wedged together that it is quarried with difficulty. This is the Keeseville variety, 

 and that of Pa. and N. J. The other, the typical mass at Potsdam, is an even 

 bedded and somewhat porous rock, at many places a distinct friable sandstone, 

 in others a yellowish-brown sandstone, the particles of which are compacted 

 together, so as to form a firm, even-grained mass, with the planes of deposition 

 perfectly smooth and separable from each other, the layers being from two inches 

 to four feet thick. At Potsdam quarries, a layer of 100 square feet may be raised 

 and split into rails, six inches wide and ten feet long, or it may be broken into 

 pieces the size of a brick, with even edges of fracture, and each layer may be 

 separated into many. The color here is yellowish-brown, and a deep red variety 

 occurs at Chazy, resting immediately upon the primitive rock. Mather, 102. It 

 is nowhere charged with mineral matter, either disseminated or in veins. The 

 native copper of Lake Superior is hi an old trappean formation, and has no relation 

 to the neighboring extensive formation of Potsdam. In an economical point of 

 view, the Potsdam is unimportant as a depository of useful substances. 



