200 [Assembly 



the different parts as uniformly mingled together as possible. As 

 a general rule, it is only in the darker stones that the coloring matter 

 has any tendency to disintegrate the mass. 



In the selection of building stones, the simple presentation of a 

 sample is not enough. The rock in place should be examined in 

 the outset ; for in its natural outcrop it has been exposed to the 

 action of the weather, in all its influences, for many thousands of 

 years. One of the principles taught in elementary geology is that 

 the soft and decomposing rocks appear in low rounded or flattened 

 exposures, or entirely covered by the soil or their own debris, form- 

 ing no conspicuous feature in the country ; while on the contrary 

 the harder rocks stand out in relief, producing marked and dis- 

 tinguishing features in the landscape. It not unfrequently happens 

 that the geologist, having familiarized himself with the succession 

 and character of the rocks of a particular locality or neighborliood, 

 b}'^ seizing the features and character of the prominent beds, is able 

 to trace them in succession along the escarpment or mountain range 

 as far as the eye can reach, and to approach them from any distant 

 point with assurance that he has not been deceived. 



The strata which make these features in the landscape are the 

 ever-enduring rocks, which have withstood the action of the atmos- 

 phere through a period a thousand times longer than any structure 

 of human origin. One cannot doubt that if properly placed in any 

 artificial structure, they would still withstand the action of the 

 elements. These escarpments, in their natural situation, may be 

 coarse, rough and forbidding, more or less dilapidated or unequally 

 dilapidated from the effects of time ; but as they there present them- 

 selves, we shall be able to see their future in any structure exposed 

 to the same influences. 



It is true, however, that no artificial structure or position will 

 ever subject the stone to the same degree of weathering influence 

 to which it is exposed in its natural position, but the same changes 

 in degree will supervene upon any freshly exposed surfaces. In its 

 natural position the bed has been encased in ice, washed by currents, 

 saturated with rains and melting snows, frozen and thawed, and ex- 

 posed to the extreme of summer heat without mitigation. The 

 rock which has withstood these influences is quite equal to with- 

 stand the exposures of a few centuries in an artificial structure. 

 Yet there are occasionally modifying influences and conditions 

 which have sometimes subdued the permanence of a durable stone, 

 and given preference to others less diu'able. It therefore becomes 

 necessar}'^ to carefully examine all these conditions, and to determine 

 not only from the rock in place, but also from its physical consti- 

 tution, whether it will meet the requirements of the structures 

 proposed. 



It not unfrequently happens, in working a quarry, that layers are 

 reached which have not been exposed to the weather, and it is then 

 necessary to test the strength and power of endurance of the stone. 

 This may be done by repeated exposure to freezingand thawing, by 



