822 -Instruction in Geological T; nvestigation. 
graphic survey of Massachusetts will, however, soon in 
concern the division of the country into its kinds; that is, s 
areal geology. As all of our region is largely drift-covered,t f 
is necessary for good’ work to map the rocks only where ti $ 
are seen in outcrops, and to classify the drift as well as tk ff 
_ rocks: beneath it. The number of formations and sub-form 
tions has to be discussed; the characteristics of all to be det | 
mined; and the boundaries to be marked out. This is so large 
a problem, and is often so complicated, that for the first twoo f 
three excursions the student may feel discouraged. ve | 
scholars learn much by working out their own difficulties, wit! 
no more aid than is given by answers to admissible question 
those with less ability and perseverance need more immediat? 
assistance. Repeated visits to the more significant localities at 
advised; for the beginner can hardly hope to reach at once ga 
ambition of the most experienced geologist, and see in a first a 
single view not only the raw facts as they then appear, but ab 
the critical points that are visible only after reflection. po i 
are indeed few fields that do not repay second and third gleaning: 
if they seem barren after the first harvest, the gleaner 
ascribe the barrenness to his own want of skill. 
-fully this is done, there will be enough work for review ei 
by later discoveries, and quite out of sight at first. ne 
matter is the need of distinguishing explicitly betwee it 
seen and what is inferred. Printed maps generally ere 
distinction on account of the large scale that it rege oe 
Omission on field-maps is inexcusable. Strong one 
lines may be used to indicate well-ascertained facts; “i 
dotted colors, and broken or dotted lines, aided by > : 
tion-points, will signify doubt. Uncolored portion’ of cou 
map should mean only unvisited country. A piece? 
carefully surveyed and mapped in this way gives § 5 
