The following rocks, from Cecil County, have been studied by A. G. Leonard. Descriptions as yet unpublished.

G. Quartz-biotite - hornblende - diorite, near the foundry on Stone Run. Granitic in appearance.

H. Quartz-biotite - hornblende-dioritę, near Porter's bridge on Octoraro Creek.

I. A true diorite with very little quartz, Stone Run, one-half mile northwest of the mill near Rising Sun.

J. Norite, three-fourths of a mile northwest of McKinsey's mill. Analyses by Hillebrand, record No. 1755.

3. GRANITE AND GNEISS.

For descriptions see Williams, 15th Ann., p. 657, and Keyes, ibid., p. 685. The Rowlandsville granite is described by Grimsley in Journ. Cincinnati Soc. Nat. Hist., vol. 17, p. 78.

A. White granite, Brookville, Montgomery County. (Williams.) B. Binary granite, Guilford, Howard County. Contains quartz, orthoclase, a little plagioclase, muscovite, and biotite, with occasional zircon and apatite. (Keyes.)

C. Biotite-granite, Woodstock. Light colored, fine grained. Quartz, feldspar, and biotite, with accessory allanite and epidote. (Keyes.) D. Biotite-granite, Rowlandsville, Cecil County. Dark colored. Contains plagioclase, orthoclase, quartz, epidote, biotite, sphene, magnetite, and apatite, with a little secondary muscovite. The percentages of the several minerals are computed by Grimsley from the analysis.

Analyses by W. F. Hillebrand, record Nos. 1220, 1422, 1455. In B and C manganese was present, barium and strontium were not tested for, and the alumina contains possible titanium and phosphoric acid.

E. Biotite-granite, Dorseys Run, Howard County. Typical, dark colored. Quartz, feldspar, and biotite, with accessory allanite and

H. The typical gneiss of the Dorseys Run area.

mentary origin.

Perhaps of sedi

Descriptions by Keyes. Analyses by Hillebrand. The remarks

appertaining to B and C apply here also.

Record No. 1220.

I. Biotite-granite, Sykesville. Contains quartz, feldspar, and biotite, with accessory magnetite, zircon, and apatite.

J. Inclusion in I, derived from limestone. Yellowish central portion. Consists of epidote and quartz, with a little chlorite.

K. Same inclusion, fine-grained dark outer zone. Quartz, garnet, and epidote, with a little magnetite. Feldspar and muscovite in some portions. Descriptions by Keyes. Analyses by Hillebrand, record No. 1220, with the same limitations as in the Guilford, Woodstock, and Dorseys Run granites.

L. Typical gneiss of Washington, D. C., from quarry of Potomac Stone Company, 1 mile below Chain Bridge. A basic granite.

M. Fine-grained, fissile, chloritic gneiss, from northwest of Cabin John Bridge. Also a basic granite.

N. Fine-grained, hard gneiss, from the second lock at the Great Falls of the Potomac. Probably of sedimentary origin.

Described by Williams. Analyses by Hillebrand, record No. 1459.

To these may be added three analyses of feldspars from the pegmatite of Jones Falls, Baltimore. Described by S. L. Powell in Johns Hopkins Univ. Circular, vol. 12, p. 49. Analyses by W. F. Hillebrand, record No. 1421.

P contained a little unseparated quartz. All three contained traces of lithia. In O and Q the traces of iron were weighed with the alumina.

Bull. 168-4