ARCHITECTURE OF FRACTURED SUPERSTRUCTURE 63 



ment of the geologist who, after a study of the district, has prepared 

 the map. Unfortunately the conventions in use are such that his 

 observation and his theory have been hopelessly intermingled 

 in the finished product. Armed with the geological map, the 

 student who visits the district finds spread out before him, it may 

 be, a landscape of hill and valley, of green forest and brown farming 

 land, which is as different as may be from the colored puzzle which 

 he holds in his hand. Hidden under the farm vegetation or masked 

 by the woods are scattered outcroppings of rock which have been 

 the basis of the geologist's judgment in preparing the map. Ex- 

 perience shows that in order to bridge the wide gap between the 

 geology in the landscape and the patches of color upon the map 

 something more than mere examination of the colored sheet is 

 necessary. We shall therefore describe, with the aid of laboratory 

 models, the various stages necessary to the preparation of a geo- 

 logical map, and every student should be advised to follow this by 

 practical study of some small area where rocks are found in out- 

 crop. 



Though the published areal geological map represents both fact 

 and theory, the map maker retains an unpublished field map or 

 map of observations, upon which the final map has been based. 

 This field map shows the location of each outcrop that has been 

 studied, with a record of the kind of rock and of such observations 

 as strike, dip, and pitch. Our task will therefore be to prepare : 

 (1) a field map ; (2) an areal geological map ; and (3) some typical 

 geological sections. 



Laboratory models for the study of geological maps. In order 

 to represent in the laboratory the disposition of rock outcrops 

 in the field, special laboratory tables are prepared with removable 

 covers and with fixed tops, which are divided into squares num- 

 bered like the township sections of the national domain (Fig. 47). 

 To represent the rock outcrops, blocks are prepared which may 

 be fixed in any desired position by fitting a pin into a small augur 

 hole bored through the table. The outcrop blocks for the sedi- 

 mentary rock types are so constructed as to show the strike and 

 dip of the beds. (See Appendix D.) 



The method of preparing the map. To prepare the map, use 

 is made of a geological compass with clinometer attachment, a 

 protractor, and a map base divided into sections like the top of 



