DEPARTMENT OF LITHOLOGY AND PHYSICAL GEOLOGY. 203 



ing more properly to the Department of Arts and Industries. The 

 stones used for abrading purposes, i. e., hones, whetstones, grind- 

 stones, etc., are shown in the forms in which they are used in the vari- 

 ous industries. The grindstones proving too bulky for our limited 

 space are proportionately reduced in size. 



B. Dynamical and Physio grai^liical Geology. — Under this section are 

 discussed the agencies and methods of geological change. It is of 

 course impossible to represent these agencies in actual operation, and 

 we must confine ourselves to a display of results which the labels must 

 explain. In this section are placed those objects illustrative of (1) 

 Plutonic or hypogene action, under which are included {a) heat as dis- 

 played in metamorphism, production of veins, volcanoes, volcanic action 

 and non- volcanic igneous ejections ; (b) the movement of the earth's 

 crust as displayed by folds and faults ; (c) cohesive attraction as dis- 

 fjlayed by crystallization, cleavage and concretionary structure, and 

 {d) the chemical processes of rock formation and metamorphism, this last 

 division comprising chemical Geology. We then pass to (2) Surface or 

 epigene action, where are displayed materials illustrative of the destruct- 

 ive, constructive and reproductive effects of the atmosphere, of surface 

 water, and of life in its various forms. The effects of atmosphere and 

 water are illustrated by specimens showing the destructive chemical 

 process of oxidation, deoxidation, hydration and solution, or the general 

 phenomena of rock weathering as displayed in the breaking down of 

 rocks and the formation of soils, and in the erosive power of water, 

 shown in part by models; while the constructive and reproductive 

 effects are shown by the formation of sand dunes, deltas, stalagmitic 

 deposits and sinters The effects of life in all its various forms is shown 

 by the wood and stone burrowing of insects and animals, by the pro- 

 tective action of algse, moss, lichens, by deposits of diatomaceous earth, 

 the formation of coral islands* and of coal, guano beds, etc. 



C. Structural Geology : The architecture of the EartWs Crust. — Under 

 this third head are displayed (1) Stratified rocks showing stratification 

 and its accompaniments, as false or current bedding, ripple marks, mud 

 cracks and foot prints ; (2) Igneous rocks, both contemporaneous and 

 intrusive; (3) Metamorphic rocks; (4) Mineral veins; (5) Surface de- 

 posits and (6) Joints, cleavage, curvature and dislocations, and other 

 modifications of the primary arrangement of the earth's crust. Many 

 objects are here displayed of precisely the same nature as under dynam- 

 ical geology, in the one case illustrating the methods by which cer- 

 tain structures are brought about, and in the other the structures them- 

 selves. 



D. Stratigraphical or Historical Geology. — Under this, the fourth 

 subdivision, is considered the chronological succession of the geologi- 

 cal formations, the rocks being arranged according to the order of their 

 deposition or ejection. From this series fossil forms are to alarge extent 



*See also Bermuda Collection to be noted later 



