THE NORTHERN PACIFIC ROUTE. 145 
but at this place it extends for only a mile or so and is cut off by a 
fault that trends about N. 20° W. and crosses the railway near mile- 
post 29. As shown on the map, this fault separates the Newland 
limestone on the east from the Ravalli quartzite on the west. 
On approaching Thompson Falls the traveler can see on his right 
a hill, and, if his eyesight is particularly good, he may be able to 
detect on its summit a steel tower erected by the United States 
Forest Service. On this tower during the summer is stationed an 
observer, who with powerful glasses watches for forest fires. As he 
can. see on all sides for a distance of 50 miles, if the weather is clear, 
he is generally able to detect a fire soon after it starts and to notify 
the nearest ranger by telephone. Forest fires, especially such as 
swept through these mountains in 1910, not only burn a great 
amount of valuable timber but may also destroy towns along their 
pathway, with considerable loss of life. Under the present system ~ 
of observers on high stations and an efficient organization for fight- 
ing fire, the destruction of timber has been greatly reduced and the 
loss of life nearly eliminated. 
The town of Thompson Falls took its name from the falls of the 
same name, which were discovered in 1809 by David Thompson, the 
explorer and astronomer of the Northwest Fur Co. 
The water here falls 50 or 60 feet over resistant ledges 
of the Ravalli formation. It is estimated that with 
proper installation 40,000 horsepower could be gen- 
erated at this fall. A dam is now being constructed, 
and electric power is to be furnished to the mountain division of the 
Chicago, Milwaukee & St. Paul Railway, 35 miles to the south. It is 
reported that any surplus power may be utilized in a similar manner 
by the Northern Pacific Railway. 
West of Thompson Falls the bluffs on the right recede so far from 
the river that the rocks composing them are unrecognizable from the 
train, but the Ravalli formation’ shows at railway level dipping 
Thompson Falls. 
Elevation 2,458 feet. 
Population 325. 
St. Paul 1,351 miles. 
1 The northern Rocky Mountains are 
made up largely and in some places 
wholly of the formations constituting the 
Belt series. These formations consist of 
Helena, Mont., and hence are known as 
the Belt series. 
95558°—Bull. 611—15——10 
Very few fossils occur in the series, and 
those that have been found bear very 
with which they should be most closely 
related. The only traces of animal life so 
£ Be $4 aor < ; or ol | 
lites are a few fragments of a small crusta- 
cean and the trails of worms. The lime- 
stones are crowded with peculiar coral- 
like forms, which Walcott has recently 
determined to ge similar to 
ftha lakes 
the algse now growing i 
of New York. Walcott concludes from 
