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| | Description of the Geology of Philadelphia County Pennsylvania (Site not responding. Last check: 2007-10-13) |
 | | A special map of the Philadelphia belt of the older and younger gneiss formations, first appearing at the surface at Morrisville, opposite to Trenton, N.J., and widening westward so as to cover most of Delaware county, will be found in this Hand Atlas, in the place of a map of Philadelphia alone. |
 | | The abundance and excellence of the Delaware valley clay has conduced to the celebrity of the Philadelphia house-brick, and its almost universal use in the construction of its houses, a comparatively small number of public and private edifices being built of marble, New Red brownstone, or Delaware county serpentine. |
 | | From: A geological hand atlas of the sixty-seven counties of Pennsylvania :embodying the results of the field work of the survey, from 1874 to 1884. |
| www.libraries.psu.edu /emsl/guides/X/philadelphia.htm (197 words) |
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