REVIEWS 277 



which exposed the ancient cores. At the base of the Paleozoic is pro- 

 nounced unconformity. During Cambrian times a land mass probably 

 occupied the northern portion of the state. South of this, fossiliferous 

 Cambrian beds rest upon the ancient complex. The sea shore moved 

 northward during the Paleozoic, and the Ordovician, Silurian, and 

 Carboniferous beds overlap the Cambrian, and extend farther north. 

 In the northern part of the state the Upper Carboniferous rests directly 

 upon the pre-Cambrian, and these conditions continue as far south as 

 Socorro. The Cambrian consists of quartzite, shales, and limestones; 

 the Ordovician is predominantly of limestone; the Silurian of lime- 

 stone and quartzite. 



The fossiliferous Devonian, represented in the western part of the 

 state, is a thin formation of clay shale, calcareous in the upper portion. 

 At some places it is believed there is an unconformity of erosion between 

 the Ordovician limestone and the Devonian, but at many places they 

 are conformable. 



The Mississippian is recognized at several places south of latitude 

 34 . The Pennsylvanian is deposited with considerable thickness over 

 the whole state, reaching a maximum between Santa Fe and Las Vegas. 

 As far south as Socorro, it consists of sandstone and shales in repeated 

 alternation with limestone beds. Farther south the pure limestone 

 prevails and the total thickness appears to diminish. All indicates 

 near shore conditions in the northern part of the state. The upper 

 Carboniferous is divisible into two groups, the upper one of which is of 

 the Carboniferous "Red Beds." Unconformities of erosion mark both 

 the top and bottom of the group. Triassic "Red Beds" are unknown 

 in the southern part of the state, but have been described in the Sierra 

 Nacimiento. 



The Cretaceous rests upon the eroded "Red Beds," the Carboniferous, 

 and the pre-Cambrian. This series consists of pliable shales which 

 once extended over the whole territory with greater continuity than 

 any other formation except perhaps the Early Pennsylvanian. 



The Tertiary was marked by igneous activity, mountain making 

 and ore deposition. First, manganitic magmas were thrust out as 

 laccolithic masses beneath the pliable, tough Cretaceous sediments. 

 Marine conditions ceased. Lake basins developed, at least in northern 

 New Mexico. Mountain building accompanied and succeeded intrusion. 

 These forces were active mainly in the belt extending southwestward — 

 the extension of the Rocky Mountain region. The pre-Cambrian core 

 to the north was forced up by faulting or by warping and faulting. 



