418 Geology . 
try what is to be done with that important part of our 
subject. 
The following circumstances have been observed, and 
may be taken as facts. 1. There appears to be a series 
of strata, or as Werner calls them formations, that may 
be considered as surrounding the nucleus of the earth. 
The first formed, or lowest series, always preserve the 
same situation to each other except where occasional 
eruptions, of circumstances not of a general nature, make 
a variety in their situations. These strata are not only 
the deepest, but they are also the highest that are observ- 
ed in the crust of the earth ; forming the tops of the high- 
est mountains. They are characterised by an appearance 
of crystallization, and by containing no remains of or- 
ganic matter, vegetable or animal. The strata or forma- 
tions that in general constitute this first, deepest, highest^ 
and crystallize^ series, are. 
Granite , consisting of feldspar crystallized in facets fre- 
quently lustrous ; quartz ; mica. Sometimes also schorl. 
Sometimes the schorl, sometimes the mica, sometimes 
both are wanting. But these are accidental deficiencies. 
This stone in all its varieties, is common about Balti- 
more, and at Germantown. 
Gneiss .—' This is a stone composed of feldspar, quartz, 
and mica, in much smaller particles than in granite ; in 
the mass, it is also stratified or formed in layers, which 
granite is not. This is the common stone used for build- 
ing, and for kirb stones in Philadelphia. 
Mica Slate . — This is a stratum or formation consist- 
ing principally of quartz and mica, in which the mica 
predominates. It generally also contains crystallized .garw 
nets. Stones of this formation are common about Ger- 
mantown, the Falls of Schuylkill, 
Clay Slate .— The common grey, bluish, yellowish, or 
smoke coloured slate, often used for covering houses.. 
