Basic Rocks of Northeastern Maryland. — Leonard. 169 
the hornblende more or less fibrous, sometimes nearly colorless 
in transmitted light, and derived from the pyroxenes. These 
metagabbros have not been extensively developed in this re- 
gion and are much less abundant than the true dioryte. As a 
rule the original hornblende rocks dififer in texture from the py- 
roxene rocks, the former being considerably coarser and re- 
sembling the granites in size of grain. 
The norytcs make up the larger part of the area occupied by 
the pyroxene rocks. They are abundant not only in Cecil 
county, but also across the Susquehanna in Harford county, 
where they are found at many points. The hypersthene-gabbro 
is probably a facies of the noryte and the two types merge into 
each other wherever they occur. But though the pyroxene and 
hornblende rocks are so intimately associated in their geological 
occurrence, no intermediate varieties connecting the two were 
found in Cecil county, such as exist between the diorytes and 
granites. An original hornblende gabbro is stated by G. H. 
Williams* to occur in Harford county, and is said to pass into 
augite or hynersthene-dioryte, but no such intermediate types 
were observed east of the Susquehanna. 
GEOLOGICAL RELATIONS OF THE NORYTES AND GABBROS TO THE 
ULTRA-BASIC ROCKS. 
The non-feldspathic rocks occur as lens-shaped masses and 
as dikes within the noryte and are also found along the border 
next to the serpentine, where the}^ seem to represent a more 
basic facies of the noryte. The peridotyte and pyroxenyte are 
closely associated in their geological occurrence and the one 
type sometimes graduates into the other. This relationship is 
well shown in the railroad cut just below Conowingo where 
both of the ultra-basic rocks are found together in the same 
dike. The olivine is sometimes confined to particular portions 
of the rock, occurring abundantly in certain layers or bands 
and being almost absent from others. There results from this 
arrangement a banded rock made up of alternating layers of 
nearly black serpentine and of little altered pyroxene — a struc- 
ture mentioned by Williams in the peridotytes of Baltimore 
county, t 
The pyroxenytes are intimately related to the norytes with 
which they are connected by intermediate types. All varieties 
* Johns Hopkins Univ. Circulars, No. 6.5. Vol. VII, 1888, p. 62. 
tBull. U. S. Geol. Sui-v., No. 2S. 1SS6, p. 57. 
