58 The American Geologist. January, 1950 
conditions would occur in the case of fluviatile deposits and may 
be considered as evidence pointing to an alluvial origin they are 
hardly to be considered as absolute proof of such an origin. 
In water of constantly varying depth there would be variation 
in the texture and composition of the beds. Because of an alter- 
nate deepening and shallowing of the water we may get a succes- 
sion of gravel, marls and gravel. A possible elevation in one part 
of the lake accompanied by depression in another part would cause 
changes in the thickness and extent of the component beds and 
might produce an erosion line. Ripple marks have been in some 
cases preserved to the distance of a mile or more from the shore 
as in the case of Great Salt lake. Cross bedding in lakes due to 
the action of counter currents has been observed and wind cur- 
rents have been effective in producing this phenomenon. Sub- 
angular conglomerate may be formed from pebbles which have been 
transportd a short distance and quickly cemented by calcium car- 
bonate deposited from the saturated water. If we assume that the 
Cerrillos peaks emerged from a lake as islands, the material for 
the conglomerate might be furnished by the erosion of these 
islands, and alluvial deposits from the mountain streams emptying 
into the lake would account for the presence of the alluvial fans 
at the base of the present mountains. 
The economic products of this region are: 
1. The anthracite and bituminous coal of the Madrid field. 
2. The turquoise deposits of Turquoise hill. These are found 
as veins and nodules throughout the augite andesyte and have 
been altered from the country rock by heated solutions and vapors 
rising along lines of fracture. 
In Part II Mr. Johnson gives a detailed account of the palae- 
ontology of the region describing with great accuracy the fossils 
collected from nine different sections. These descriptions are illus- 
trated by a fine series of plates which add greatly to the interest 
of the book. The whole article shows evidence of the most care- 
ful and accurate work. 
In Part III five series of rocks are described: 
1. The mica-andesyte forming sheets interstratified with 
shale. 
2. The eruptive breccias of the Galisteo group. 
3. The hornblende-andesyte forming the older and smaller 
laccoliths. 
4. The augite-andesyte, which is the most abundant rock of 
the Cerrillos district and which forms the main part of the lacco- 
litic uplift. 
5. The olivine basalt which forms the lava flow of Mt. Cal- 
vary and occurs in radial dykes as the basic limburgyte. 
Mr. Johnson has classified the Cerrillos rock under the chemico- 
