TYPES OF FOREIGN INCLUSIONS 93 



extent. I have described only the fine exposures at Greenfield and 

 Meriden in a paper published in this journal.* 



TITANS PIER TYPE: B LENDING OF MUD AND SAND WITH THE LAVA AT THE 



SURFACE OF THE BED 



I have also described with some detail another extensive area within 

 which the great Holyoke trap sheet, here about 400 feet thick, is over 

 large patches both at its upper and its under surface contaminated 

 by foreign sedimentary material, which was for the most part marly and 

 is now consolidated into a dove-colored limestone, more rarely into a 

 shale or sandstone. For 10 miles or more along the sheet from Titans 

 pier on the Connecticut to the Holyoke- Westfield railroad (see plate 24) 

 nearly every lower contact shows this contamination for 10 or 12 feet up, 

 and it is present over large portions of the upper surface; almost every- 

 where indeed where it seemed probable that the exact upper surface was 

 exposed. 



The results are very different from the case described above. Every- 

 thing is in accord with the hypothesis that the great highly heated trap 

 sheet flowing beneath deep water caused ascending and consequent con- 

 vection currents, by which the adjacent fine-grained marly or muddy 

 sediments were quickly swept over the congealed surface of the trap, 

 and by the disturbance of this thin crust (which disturbances sometimes 

 went so far as to break it up into blocks which careened and sank into 

 the liquid mass) much of the fine mud was quickly mingled with the 

 liquid lava under such pressure that the two were stirred together like 

 two immiscible fluids. This sometimes produced a perfect emulsion, 

 great swarms of drops of the marly mud being carried down into the lava 

 and appearing now as dove-colored spheres of limestone. Sometimes each 

 sphere is white for a small segment at its upper surface which represents the 

 cavity formed by the settling of the mud and which is now filled by the 

 later infiltration of calcite. In these cases the cooling has been so rapid 

 that no augite has formed in the adjacent trap, but all the iron has 

 solidified as magnetite in a fine powder which is greatly concentrated 

 in a band i millimeter wide adjacent to the fragments and cavities, thus 

 showing a distinct differentiation. Much more frequently the limestone 

 and the trap are so intricately blended that both must have been en- 

 tirely fluid at the same time and under such pressure that the moisture 

 could not expand and make the mass scoriaceous. At the other extreme 

 the trap, already solid and porous, has been shattered by small explosions 

 and its angular fragments have been cemented i>y the mud. Of course 

 all intermediate stages can be observed. 



♦Diabase pitchstone and mud enclosures of the Triassic trap of New England. Bull. Geol. Soc. 

 Am., vol. 7, 1898, pp. 59-86, plates 3-9. Geology of Old Hampshire county, 1898, pp. 419-439. 



