M. Godon’s mineralogical observations. 149 
* 
laminary felspar, often with an aspect somewhat greasy ; grains of hy- 
aline quartz, commonly uncoloured ; small particles of amphibole ; 
and sometimes a green substance, which is epidote. 
4. Nodules of petrosilex involving small crystals of felspar, and 
sometimes grains of quartz, and presenting a perfect analogy with 
some porphyritic petrosilex above mentioned (25); whence I have 
drawn the specific name of porphyritic. 
34. The nodules or kernels, which compose this rock, have some- 
times more than a foot diameter [Brookline], with almost al- 
ways an orbicular or elliptical figure. Those, which present a polye- 
drical form, have their angles commonly rounded. These nodules are 
closely fitted and joined together, without leaving any empty spaces. 
They are not united by a cement ; for, notwitstanding the aspect of 
some varieties of this rock, the naked eye may observe, that the spaces 
which exist between these kernels, are filled, not with an homogene- 
ous paste, but with small comminuted fragments of minerals of the 
same nature as the large one. Sometimes the kernels present an uni- 
form and progressive size, down to that of” sand stone, and from 
these this rock, in an insulated specimen, may be confounded with a 
free stone. I give to it the designation of granulated. 
35. The surface of this rock, in contact with the air, is soon alter- 
ed. The felspathic and petrosiliceous parts moulder into clay, and 
the quartzose nodules, with commonly a rough surface, remain in pro- 
jecture, or come off, leaving empty the cells, in which they were includ- 
fs ; 
It falls commonly into vast polyedrons, the faces of which are some- 
times smooth, as if they had been polished by the friction of a stream 
of water. . 
- This rock often contains veins, sometimes very thin, of white hya- 
