Another interesting contact

Today the high rate of drilling penetration continued, we processed core down to 450 ft.  In doing so, we eventually saw the end of the massive unit mentioned in yesterday's update: it was almost 100 feet thick!  Our best initial interpretation is that it is an intrusive body, probably a sill.  The picture below shows the bottom contact of this unit with the underlying thick soil or ash layer that it invaded and baked. 

Note the entrainment of the underlying unit, a classic intrusive characteristic.  In addition, the dark region at the center of the photo is incredibly fine-grained, almost glassy.  This indicates that the rock cooled very quickly here along the lower margin of the unit, the underlying material may have been wet and aided in this cooling.

The last unit we looked at today was highly vesicular and had lots of olivine, more than any units we've seen so far...every day we see something new and interesting!