,j.) GEOLOGY. 



snrin^s which do not erupt, but regularly contain water, at the tem- 

 perature of 200 degrees of Fahrenheit, and are used by the Icelanders, 

 for boilinf, washing their clothes, and other domestic purposes. It has 

 been calculated that, during an eruption, one of these geysers throws up 

 59,064 gallons of water every minute. Numerous hot-springs exist in 

 the bed of a considerable river, and the quantity of boiling water they 

 emit is so great, that it cannot be kept under by the cold water of the 

 river, but forcing its way upwards, it bubbles and spouts above the 

 surface of the stream. The mechanism of these geysers must be simple 

 to have lasted for so many ages. They are mentioned by Saxo in his 

 history of Denmark, and this shows that they must have existed for about 

 six hundred years. 



GEOLOGY. 



The name is derived from two Greek terms, oea, the earth, and 

 logos, a discourse; and its object is to investigate the nature and 

 properties of the substances of which the solid crust of the earth is 

 composed ; the laws of their combination, as constituting the elements 

 of rocks and other stony masses ; the arrangement of these different 

 masses, and their relation to each other ; the changes which they appear to 

 have undergone at various successive periods ; and, finally, to establish a 

 just theory of the construction of that solid crust. A large portion of the 

 solid materials of the earth is arranged in beds, varying in extent and 

 thickness, but everywhere indicating the operation of one common agent. 

 These beds are sometimes slightly coherent, as when composed of clay 

 or sand : but at other times they are consolidated stony bodies, arranged 

 in parallel layers, which are often subdivided into thinner portions, by 

 seams or joints, and preserve their parallelism for a great extent, 

 whether their position be horizontal, or at different degrees of inclination. 

 Such beds are termed strata, and the general fact is expressed by the 

 term stratification. Sometimes we find a succession of strata of the 

 same rock in juxta-position : at other times there are strata of different 

 substances, interposed or alternating with the principal rock. The 

 position of strata in plains is generally but little inclined towards the 

 horizon; butasweascend mountains, the strata are usually inclined, some- 

 times nearly or even absolutely vertical. When a mountain or chain of 



