April, 1928 



EVOLUTION 



Page Seven 



and west, notably in southern Eurasia, reduced the north 

 and south circumference and pressures. 



Also, in solidifymg, the substratum becomes denser. 

 Upon this denser support, the continental scum again 

 floats high. As the continents rise relative to the ocean 

 levels, the shallow, transgressional seas retire from the 

 lowlands. The continental masses underlying these seas, 

 hitherto forced deep into the substratum by the increas- 

 ing weight of the accumulating sediments, are now slowly 

 uplifted by the denser substratum. Just where the water- 

 laid strata are thickest, there will be upheaved the great- 

 est mountain ranges. So we find sea beds and their fos- 

 sils on the highest of mountains. With our modern 

 knowledge of geology, we can understand this without 

 straining piously over any absurd flood story. 



A Series of Geological Cycles 



We have clear evidences, gathered by the patient and 

 exacting labors of the geologists, that five or six of these 

 great cycles have occurred in the decipherable history 

 of the earth. We are ourselves at the beginning of a 

 period of slow heat accumulation which must in the re- 

 mote future, as in the past, culminate in another geologic 

 revolution of crustal tides and heat escape, of trans- 

 gressional seas and birth of mountain ranges. The whole 

 story canot be told in these brief sketches, but the main 

 events, with the related story of organic evolution, will 

 be outlined in the next article. For the details and sup- 

 porting evidence, the reader is referred to John Joly's 

 "The Surface History of the Earth." 



Proofs of Evolution from Geology and 



Palaeontology 



By Hugh F. Monro 



GEOLOGISTS have classified about two hundred and 

 fifty thousand feet of rocks as comprising the 

 known thickness of the earth's crust, although its ac- 

 tual thickness is much more, the lowest or Pre-Cam- 



brian layer being of unknown extent, 

 pressure have profoundly modified the 

 rocks, as evidenced by their structure; and no 



(or at least very doubtful) indications of life 

 are found. Such rocks as granite and basalt 

 have undoubtedly been formed directly by the 

 cooling of molten matter and naturally fur- 

 nish no trace of organic remains. Next come 

 the great Huronian series, a thick group of 

 sedimentary rocks containing considerable in- 

 direct evidence of life (e.g., limestones) and 

 some problematical fossils. Then comes a 

 transition series, the Belt Terrane. containing 

 undoubted through fragmentary fossils. The 

 lowest rocks of the next series (Cambrian) 

 form the lowest stratum of the Palaeozoic or 

 Primary Era and here are found the first 

 abundant traces of life. These traces are of 

 the simpler kinds of organisms, the inverteb- 



ates, and are onlv found in sedimentary 

 rocks that have been formed 

 by the accumulated detritus 

 derived from preexisting 

 rocks. The duration of the 

 Pre-Cambrian era must have 

 been as long as all the suc- 

 ceeding epochs put together, 

 and the total lapse of time 

 since the beginning of the 

 formation of the sediment- 

 ary or stratified rocks (includ- 

 ing the Pre-Cambrian) would 

 be at least 100.000.000 years. 

 Ascending the geological 

 scale, we find fishes first 



Heat and 

 Archaean 



appearing in the Ordovician strata, then successively 

 Amphibians in the lower Carboniferous, reptiles in the 

 upper Carboniferous, birds in the Jurassic, mammals 

 in the Triassic, and man in the most recent or Pleis- 

 tocene formation, which is about 4,000 feet thick. 

 If it is true that all existing species have descended 

 by a process of modification from other species fewer 

 in number and simpler in structure, then it is to be 

 expected that some of the intermediate links could be 

 found, notwithstanding the admitted imperfections of 

 the known geological record. And such is the case. 

 The cynodonts of the Permian and Triassic of South 

 Africa link the reptiles and the mammals; Archaeop- 

 teryx of the Jurassic links the reptiles and birds; 

 Deltatheridium of the Cretaceous links the placental 

 mammals with the more primitive mammals. 

 The fossil histories of cephalopods. horses, 

 rhinoceroses, elephants and camels have been 

 fairly well traced and numerous connecting 

 forms discovered, the most complete being 

 that of the horse, whose peculiar one-toed 

 hoof readily lends itself to popular explana- 

 tion. Our knowledge of this extremely inter- 

 esting series, largely due to 

 the late Prof. 0. C. Marsh, 

 has been ablv summarized bv 

 Dr. W. D. Matthew. The horse 

 family originated from the 

 Condylarthra, a group of five- 

 toed ungulate mammals, 

 which appears at the base of 

 the Tertiary. The evolution of 

 the horse took place chiefly 

 in America. A summary his- 

 tory of the fore foot is shown 



All outside views showing the mi.idle and outer digits of tho forefoot. In Eoltip- jn the llluStration frOm UlC 



/jiw tlie two outer toes (digits IV and V) are complete. In Meiohippwi, digit V is ^ . _ -. r 1\T i 



reduced to a small Bplint and digit IV is notably smaller than the middle digit. In American MuSCUm 01 iNatUral 



Menjdupputi. digit V isaiiny nodule of bone and digit IV iias become very slender in Hisfnrv 



comparison witti the middle digit. In Eqims digit IV is reduced to a long splint, *' 



»hile o( the fifth digit no trace remains (Continued in liext ISSUS) 



FIG. 3. BTOLUTION OF THE FORE FOOT PEINCIPAL STAGES 



(Kight lo Left) 



1. t'our-toi^ri horse Eohipioi.'. ttw^'etip ICooi-h 

 2 K.iily thrco-tocd lionjc .l/i.<.^'iipp'..' Oliifocend l^porb 

 ;< Luler tliree-loml borae Jl/frycAtppiM. Miocene Kpoeh 

 I Ono-toed horse Bquut. Plwistoi-cne Hpoch and Moderi 



