II4 MINERALOGY AND LITHOLOGY. 
Barker to be argillitic mica schist, since on analysis the specimens yielded 
no magnesia. They were supposed to be talcoid because they had a 
soft-soapy feel, and an appearance of talc. These schists are widely 
distributed, while the talc schists are much more local occurrences. 
43. SERPENTINE [Mg? Si? O" +2 H? O] 
Serpentine is not a common mineral in our state. It is found in small 
amounts in some chloritic rocks of the Connecticut valley, and Mr. Hunt- 
ington has observed it at Pittsburg. It is found in light green granular 
layers or aggregations, which are either interstratified in the rocks, or scat- 
tered irregularly through them. Again: in some of the trap rocks, serpen- 
tine is a microscopic product which results from the alteration of olivine. 
As serpentine, wherever found, has the microscopic appearance of being a 
product of alteration, so, in thin sections, it has not the properties of an 
original crystal, but its optical behavior is that of an aggregate. It gives 
bright colors when revolved between crossed Nicols, but shows no other 
crystalline characters. Its microscopic appearances are various, and de- 
pend much on the mineral from which it is derived; but no extensive 
material for its study is offered in our state. 
74. Kaotin AND Ciay [AP Si? O7 -+ 2H? O]. 
Products going under these names abound all over the state. Kaolin 
is the mineral species to which they must be referred, although in a pure 
state it is not common. Kaolin is formed in all granitic regions by the 
decomposition of feldspar. In the Southern States, below the limit of 
glacial action, where the resultant products have often remained in place, 
there exist immense beds of soft rock composed essentially of quartz and 
kaolin; but in our section, where the glaciers broke down and removed 
all such decomposed materials, the kaolin is found in the lowlands mixed 
with pulverized quartz, forming the clay beds. Under the microscope, 
the composite nature of clay becomes very evident, yet the kaolin is 
often seen to be in minute crystalline scales. This crystalline character 
of the kaolin of clays was first pointed out by S. W. Johnson and Blake. 
Kaolin is orthorhombic. That the particles are crystalline is easiest 
seen by noting that they are double-refracting, and give colors between 
crossed Nicols. Besides quartz, our clays contain ferruginous materials, 
