468 C. W. HAYES — COOSA VALLEY IN GEORGIA AND ALABAMA. 



undetermined thickness. The upper portion of the Indian mountain 

 section closely resembles that on Big Cedar creek. No fossils have yet 

 been found in any member of the Weisner formation, and hence its 

 exact position is not determined, but it probably corresponds to the 

 whole or at least the greater part of the Rome sandstone. 



In the early geological study of this region the rocks underlying the 

 Coosa valley were believed to be older than the Rome sandstone and to 

 rest conformably beneath that formation. A study of their fossils, how- 

 ever, has shown them to be of the same age as the Connasauga shale, 

 and hence younger than the Rome ; also more careful examination has 

 revealed the presence of the Coosa fault, separating the rocks of the 

 Coosa valley from the Rome sandstone and other formations to the 

 south. 



Owing to the extensive deposits of silt and gravel which occur in the 

 Coosa valley, and also to the extremely complicated structure, all at- 

 tempts at subdivision of these rocks and mapping their distribution 

 must be in a large measure unsatisfactory. In a ver}?- general way they 

 may be divided into three groups, although they present so wide varia- 

 tions in lithologic character on opposite sides of the valley that the sub- 

 division is of doubtful value. 



The upper division, which generally comes in contact with the Rome 

 sandstone along the Coosa fault, there consists of characteristic greenish 

 silicious shales. In some cases the shale is replaced by greenish mica- 

 ceous sandstone, which is always highly contorted and crushed into a 

 series of lenticular masses from a fraction of an inch to four or five inches 

 thick. The sandstone is always filled with cracks or fissures which have 

 the appearance of having been produced by contraction of the strata. 

 At the surface these cracks are partially filled with quartz and where 

 they are unweathered the remaining space is occupied by calcite. The 

 sandstone is confined to the southern border of the valley. Passing 

 northward the silicious beds become fewer, being replaced by fine olive- 

 green shales, and throughout the central portion of the valley this divis- 

 ion is represented by shales in which occur numerous flat concretions 

 composed of gray silicious material intermediate in character between 

 fine-grained quartzite and chert. As the shale weathers, these concre- 

 tions accumulate upon the surface, and closely resemble well worn river 

 gravel. Along the northern border of the valley this division becomes 

 very much more calcareous. The concretions are similar in appearance 

 to those above described, but are composed of very sihcious limestone. 



The intermediate division of the rocks of the Coosa valley is com- 

 posed of clay shales, but contains in addition varying quantities of lime- 

 stone. The latter appears in some places as a few thin beds scattered 



