248 Messrs. Jackson and Alger on the 
which rise in many places perpendicularly to the height of three 
hundred feet, exhibit very distinctly, as we pass them, the parallel 
disposition of the different beds of which they are made up. 
The precipice at French Cross, from its being accessible at low 
water, is perhaps as instructive as any. Here the lowest bed, 
which is about twenty feet thick, is a reddish amygdaloid, largely 
impregnated with spheroidal zeolites; the next is an amygdaloid 
of common appearance, and contains but few minerals in its 
composition, although it presents many cavities unoccupied. The 
third is rarely vesicular, and seems in fact to pass into amorphous 
trap. The fourth and last is composed of tabular and columnar 
trap rising in irregular columns to the top of the precipice. They 
all incline away at an angle of from five to ten degrees with the 
horizon, and are distinctly separated from each other throughout 
their whole course. 
The stratified arrangement of these rocks is, we believe, an 
‘uncommon occurrence; at least, we do not remember to have 
seen it noticed but in a very few instances. Dr. M’Culloch has 
recorded an instance of it in his interesting paper on the Island 
of Staffa,* but there the precipice consisted entirely of the colum- 
nar rock, and the three beds composing it did not exhibit that 
peculiar relation of contact which distinguishes the one we have 
mentioned; nor did the precipice, compared with this, attain 
any thing like an equal altitude ; and it would be much less diffi- 
cult to assign the origin of three beds, which exhibit such similar- 
ity in structure, to one and the same epoch, than four which pre- 
sent great diversity in structure and mineral contents. They all 
appear to have been deposited at successive periods, and so long 
* Transactions of the Geological Society of London, Vol. II. p. 504. 
