182 CLASSIFICATION OF FORMATIONS. 



action of fire, and are not stratified. The terms primitive and 

 transition have been applied to these formations, but, as they are 

 inexact, they are going out of use. 



2d. Sedimentary formations, which are deposited by the action 

 of water, and are stratified. 



2. MASSIVE, or IGNEOUS FORMATIONS escaped from the earth in 

 a state of fusion, and became solid by cooling, but without being 

 stratified. They are divided into two classes : 1st, those crystal- 

 line rocks which are not traceable to the crater of any volcano now 

 recognisable, such as granite, trachyte, &c. ; 2d, massive rocks of 

 a slightly crystalline structure, traceable to volcanoes, such as 

 modern and ancient lavas, and basa'ltic formations. 



3. SEDIMENTARY FORMATIONS are arranged according to their 

 relative antiquity : they are divided into groups, composed of those 

 which appear to have been formed either at the same epoch or 

 during a geological period, during which the general condition of 

 the earth appears to have undergone no important change. These 

 formations are commonly divided into five groups, namely : 



4. First. Primary stratified rocks, in which neither organic 

 remains, nor fragments of the most ancient rocks are found ; this 

 group includes gneiss, mica-schist, quartz, transition limestone, 

 and argilla'ceous schist. 



5. Second. The transition formations, which rest on the pri- 

 mary stratified rocks, and contain fossils of plants or animals, but 

 which appear to have been deposited prior to the creation of the 

 most perfect beings of either kingdom, and only contain the remains 

 of aquatic animals, which are all very different from those of our 

 times, such as tri'lobites (fig. 4, page 28). This group includes 

 fossili'ferous schists, transition limestones, &c. 



6. Third. The secondary formations were deposited at periods 

 less remote than the transition, and consequently rest on beds of 

 the latter, or on primary rocks ; but they go back to a time when 

 the state of the globe was very different from its present condition ; 

 very few mammals then existed ; ammonites are among the most 

 characteristic fossils of the secondary formation : 



The secondary formations are subdivided into, 



1st. The carboni'ferous, which includes old red sandstone, mountain lime 

 stone, and coal : 



2d. The sali'ferous, embracing new red sandstone muschelkalk, and 

 varisgated marls, forming the tria'ssic system : 



2. What are the divisions of the igneous formations ? 



3. How are sedimentary formations arranged ? How are they divided ? 



4. How are primary stratified rocks characterized ? What rocks are 

 included in this group? 



5. On what do the transition formations rest ? How are they charac. 

 terized ? 



6. On what do the secondary formations rest ? What are the most cha. 

 r jcteristic fossils of the secondary formations ? How are they subdivided ? 

 What are the divisions ? 



