NATURAL HISTORY OF THE DIATOMACEvE. 417 



plishment of their labors. To properly comprehend the structure and 

 modes of formation of strata, be they made up of solid rock or more 

 loosely aggregated material, he must be a mathematician of no low order. 

 To understand the how, the why, and the where of the great stone book 

 laid open to his eye, to read aright the record of the rocks, he must call 

 in to his assistance at least the learning of the physicist, the chemist, and 

 the biologist,, if he be not — which, in our present and ever growing state 

 of knowledge is practically impossible — a physicist, a chemist, and a 

 biologist himself. But as it would be evidently impossible for any one 

 man to be thoroughly skilled in all these branches and their various 

 ramifications at one and the same time, the advanced and advancing 

 geologist of to-day carries out the following special plan, when engaged 

 in the study of any tract of country. He secures the cooperation of a 

 number of specialists, persons who have devoted their time and attention 

 more particularly to the study of distinct sections of science, so that 

 the highest skill shall investigate for him the several parts of the work, 

 and thus individual bricks will be contributed to the edifice which 

 the geologist desires to erect. To this end he is aided by at least a 

 chemist, who analyzes for him his rocks, his metallic ores, his marls, 

 or his soils; a zoologist, who studies the animals found in the section 

 of country gone over; and a botanist, who turns his attention to the 

 plants discovered in the district traversed. If he desires to carry his 

 investigations still further, or if the particular section of country over 

 which his labors extend requires that he should do so, he calls in to his 

 assistance individuals who have turned their attention to particular 

 branches of chemistry, of zoology, or of botany. Thus, insects may 

 abound in his field of work, and the farmers will like to know something 

 about the ravages they commit upon the crops ; or, vegetable diseases 

 may afflict those crops ; or, the rocks may be of a kind made use of in 

 building; or, remarkable kinds of deposits, of great interest to science or 

 of value in the arts, may occur. In all of these, or any similar cases, it 

 will be necessary that the subjects should be investigated by competent 

 observers, and they must be found, and their cooperation secured. Where 

 the geology alone, as restricted by the boundaries which limited it a few 

 years back, is considered, but few of these speciaUsts will be required to 

 assist. But, at the present day, and, more particularly, as is the case 

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