over the New Haven Region. 347 
West Rock Ridge or from some part of the Mount Tom range* 
to the north; for the more eastern trap ridges are too far east. 
They are, for the most part, alike in consisting of fine-grained 
_ much-rifted trap, the variety that occurs only as the outside of 
f 
the ejected trap-masses where the melted rock was rapidly cooled 
against the sandstone or air. Hence they probably came from 
the ‘op of the ridges, for the sloping eastern side is now usually 
under sandstone to within 100 feet (in height) of the top, and 
the western is that of the bold columnar front. 
The trap ridges projected upward into the ice abruptly, several 
hundred feet—the Mt. Tom ridge (or that from Meriden to Mt. 
tom in Massachusetts) probably 600 to 900 feet; a most favor- 
able condition for the successful rending and grasping work of 
that of the more eastern trap range is generally a hydrous or 
chloritic kind, very decomposable, and having usually only small 
chips as its fallen masses, This is one reason why large trap 
bowlders are rare to the eastward. 
was between S. 22° W. and S. 12° W.—the latter if from the 
northern half of the ridge. 
The 1200-ton bowlder, near the top of the Woodbridge bor- 
der, was probably from nearly the same source, the rock being 
closely the same; and its course was therefore between S. 
24° W. and S. 16° W. If the former, it had passed over the 
West Rock ridge, at a height of at least 500 feet ; if the latter, 
its Course was west of this ridge. ; 
Supposing, in the ease of each of these bowlders, the height 
. of it, a mile and a half farther south (on the grounds of 
Mr. Donald G. Mitchell). It is about 120 feet above the sea- 
level—which indicates a sinking in the ice, after passing the 
*The Mount Tom range of trap extends north from Meriden to Mt. Tom in 
Massachusetts. See map, Plate v, in volume xxiv, of this Journal, June, 1883. 
