372 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



brittle autlu-acite whose rouuded surfaces indicate that it came into the 

 fissm-e as a bitumen, but which gives a yeUoTv flame for an instant only 

 and then bums with extreme slowness. 



This is often coated by a layer of pyrites of very modern growth. 

 Where the same beds are crossed by the Chicopee River the red shales 

 contain broad seams of a pink, transversely fibrous calcite, and in the bed of 

 the Westfield River, in West Springfield, all the occurrences detailed above 

 are repeated and the curious salt pseudomorphs described on page 389 

 are also foimd. 



THE DIABASE. 



The great Deei-field and Holyoke diabase beds and the posterior or 

 Talcott bed fall into this series, but lie partly intercalated in each of the 

 above members and partly on their borders. They are described in 

 Chapter XIII. 



The series of newer volcanic cores, of which the Black Rock may be 

 taken as the type, close the list of Triassic deposits. They are specially 

 described near the end of Chapter XIII. 



THE FOKIHATIOX OF THE BASIX AXD THE DISTRIBUTION OF THE 

 SEDIIMENTS BY STRONG TIDAL CURREINTS. 



The rocks which have been described are not clu'onologieally succes- 

 sive in the order given, or in any order, but are synchronous facies, depend- 

 ent for their variety on the varying character of the shore rocks from which 

 they were derived, on the strength and direction of the tidal currents by 

 which they were carried, and on the vaiying distance from shore and the 

 varying depth of water in which they were deposited. The last is a most 

 important element. Because of the great depth of the western portion of 

 the basin and the abundance of granite along the western shore, the 

 advancing waters may have begun to deposit the arkose here a little ear- 

 lier than the other varieties, but very soon must have come in contact 

 with the argillites and schists of the eastern border, and the development 

 of the arkose and that of the conglomerate were then strictly synclu-onous. 

 As the waters rose and attained greater width the central portion of 

 the basin was occupied by a deposit of offshore sands — the Longmeadow 

 or fucoidal sandstones — and when the maximum width was reached 

 the middle portion of the sandstones sank to the fine-grained sand and mud 

 beds which have become the central Chicopee shales. 



