2l6 MINERALOGY AND LITIIOLOGY. 



Mt. Washington. The lamination is sometimes quite even; but, again, its 

 l^lane is waved, twisted, l)ent, and knotted in various ways. This variety 

 of mica schist is the ordinary one among the highly crystalline strata. 



At some points, as, for example, at Bedford, the mica is in little scales, 

 and is mostly biotitc. This brings the quartz into prominence by the 

 contrast of color. Sometimes, as at Wakefield and Japping, the crystals 

 of the ingredients are so small and so intermingled, that the rock becomes 

 nearly massive, and resembles certain basic eruptive rocks in hand speci- 

 mens. A glance with the microscope tells the true nature. This type 

 is more characteristic of the valley formations, where all the rocks seem 

 to have been recrystallized under gentler agencies than were those which 

 have heaped up the most highly crystalline strata in the mountains. 

 Some schists in this valley appear to be half fragmental in type, and 

 consist of schistose masses of sand bound together by scales of mica, and 

 resemble itacolumite in a degree. 



Andahisite Mica Schist. In this rock crystals of andalusite are promi- 

 nent and characteristic. Such schists abound in the mountainous re- 

 gion. Rarely the andalusite is quite well crystallized. Often it exists in 

 rounded nut-like forms in the rock, which are very hard, and become 

 prominent on weathered surfaces on account of their greater ability to 

 resist decay. Often it is in long rude imperfect crystals, which arc 

 heaped together in tangled web-works. These crystals often decay in a 

 peculiar manner. Sometimes the centre rots away and a cylinder is pro- 

 duced, and sometimes both centre and outside resist while the rest of 

 the crystal gives way. At some points the macled structure is very 

 prettily developed, but where this is the case the schist loses its marked 

 micaceous character and becomes argillitic. The condition of internal 

 alteration, which is shown by the microscopic structure of andalusite 

 crystals, has been already pointed out on page io6. In a microscopic 

 section of a schist from the Notch, it is seen that besides the large crys- 

 tals there arc very minute crystals of andalusite. 



Fibrolite Mica Schist. Mica schist full of fibrolite is abundant in the 

 same regions as is andalusite schist. Fibrolite ajopears to be much more 

 stable than is andalusite, and consequently its fibres appear very clear 

 and fresh in thin sections. Fig. 3 on PI. 8 represents a section of a fibro- 

 lite schist from the Notch, as it appears between crossed Nicols. In the 



