Correspondence. 325 
to the gulf of Mexico, passing tlirt)ugh Pennsylvania. The whole Appa- 
lachian sea was drained off and became dry land, a continental area of 
coal measures, much of which has since been carried away, but much 
still remains, constituting the extensive coal fields of the present time. 
The whole rain water drainage was reversed. The Palteozoic river sys- 
tem, which came from the east, disappeared and a new Mesozoic river 
system began to dissolve the raw continent and carry its undried strata 
piecemeal eastward into the newly-created basin of the present Atlan- 
tic ocean." (p. 48.) 
In the discussion of the Azoic rocks the statement is made that as far 
as the Pennsylvanian region is concerned, the irregularity is so great 
that it has been impossible "to classify its rocks into a series of forma- 
tions, or even to show with any satisfaction the course of the outcrops 
on the map. All that can be said about them is that they are a badly 
crumpled-up mass of strata, of unknown thickness, all more or less thor- 
oughly crystallized, of every grade of thick and thin-beddedness, of 
every tint of gray from nearly white to nearly black, with nearly every 
possible mixture of quartz, feldspar, hornblende, magnetite and mica, 
some of them being a syenite, some a granite, some a granulite, some a 
hornblende-schist, some a mica-schist, some a magnetic iron ore: and 
all of these kinds jmssing into one another, and overlying one another, 
as if the original sediments (if sediments they were) were of the most 
mixed and varied character, yet all derived from essentially one source, 
and belonging to (jne age, an age, moreover, not over-rich in lime and 
magnesia, if we may judge of it Vjy the absence of crystalline limestone 
beds and beds of talc or serpentine." (pp. 67-68.1 
The Architan rocks are considered to be partly of volcanic and partly 
of sedimentary origin, and the argumeiits for or against each theory are 
very fully examined. Th(^ term Huronian as applied to a certain series 
of rocks isc(msidered to Vje applicable only to those rocks exposed along 
the northern boundary of the United States. "'Should a similar series 
appear in some (jther region and be called Huronian on accovint of the 
resemblance, the name would have no time-value whatever; unless we 
should imagine that in a .so called Huronian age the whole surface of the 
planet was stuccoed with a certain formation: and received successive 
coat f of other kinds of rocks in after ages. And in fact this is a popu- 
lar view, but absolutely false." (p. 157.) 
So Prof. Lesley goes on to state what seems to be so often forgotten 
when strata of widely separated regions are correlated, how improbable 
it is that the sediments of two organic basins would be similar, remark- 
ing: '"If Huronian strata existed elsewhere [than in the typical legion] 
it would be around the Laurentian mass of the Adirondack mountains, 
in northern New York. liut they are not to be found there. To say 
that they once covered the granite and gneiss of that country, but luive 
been removed, would he to beg the question. It is not to Vie imagined 
that 18,(X)0 or even 10,000 feet of such rocks could be removed without 
leaving a trace behind. The small exhibition of specular iron ore and 
slate in St. Lawrence county can not be accepted as an equh'alent of 
