PRIMARY STRATA. 
45 
enquiries; und if it deals with rigoious 
facts alone, yet there are am(3ng them truths 
stranger than fiction.” 
The distinctions usually made between 
strata, may be therefore regarded as being 
established upon the joint evidence of min¬ 
eral differences and organic contents. 
One important class of rocks is univer¬ 
sally destitute of all traces of former life. 
This is a discovery of the old geologists 
which their successors have not been able 
to set aside; Granite, and the rocks of 
similar structure, are in this condition, and 
so are gneiss, mica-slate, and some other sub¬ 
stances which nevertheless occur in layers 
like the fossiliferous rocks. The granitic 
series bears the impress and marks of former 
fusion. Basalt, greenstone, porphyry, and 
similar substances, are usually termed trap 
rocks^ and are for the most part analogous 
to the modern volcanic products, lava, tra¬ 
chyte, and pumice. The non-fossiliferous 
slate rocks are found resting against the 
granite, or forming the base of a platform 
of fossiliferous deposits. 
Although the moderns have not removed 
non-fossiliferous rocks from the catalogue. 
