410 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



cialh' valuable because of the reproduction of all the sections and dia- 

 grams explaining earlier views of the structure of the trap ridges and of 

 the full discussion of previous theories. Of the abundant original observa- 

 tions only two groups relate to the Massachusetts area — one to the Turners 

 Falls, the other to the ]\Iount Tom region. He considers part of the trap 

 masses to be contemporaneous beds and part to be true dikes, but adduces 

 only cases under the first category from Massachusetts. The Deerfield 

 bed he makes to be three beds, echeloned one posterior to the other. I 

 have found it to be a single bed, faulted several times at the north end, as 

 will be detailed below. 



In 1892 the author published a preliminary paper on the quarry ror 

 road material at Greenfield and described the under-rolling of the ti'ap and 

 the formation of breccia-like beds.^ 



In the summer of 1896 the author presented a })aper before the Geolog- 

 ical Society of America entitled, " Diabase pitchstone and mud inclosures 

 of the Triassic trap of New England."- The paper explains the manner in 

 which water and mud, frothing up into the trap from the sea bottom over 

 which it was flowing, produced pitchstone and shattered the mixture and 

 recemented it with an aqueous deposit of albite and bisilicates. There 

 was also described the sweeping of fine mud out over the surface of the 

 Holyoke sheet by convection ciuTents and its under-rolling to form the 

 base of the bed. 



THE THREE EPOCHS OF ERUPTIVE ACTIVITY; GEKERAE ACCOITSTT. 



1. The rapid transgression of the Triassic waters over the area had 

 spread a great tliickuess of coai'se granitic debris when two fissures allowed 

 the passage of gTeat volumes of basic lava to form the Deei*field and Holyoke 

 diabase sheets. Sedimentation went on uudistm'bed. Generally the first 

 layers spread on the surface of the sheets were the same or neai'ly the same 

 as those on which the trap rests. In the Holyoke bed one can see in small 

 degree the influence of the shallowing of the waters, and the beds above 

 are of finer grain. The fissure for the Deerfield bed must have been 

 beneath the present outcrop or the lava must have come from the dikes 

 in the gneiss along- the eastern border of the basin. The fissure of the 



I Am. Jour. Sci., 3d series, Vol. XLVI, p. 146. 



- Bull. Geol. Soc. America, Vol. VIII, 1897, pp. 59-96. 



