limestones and limestone breccias of Middle Cambrian to Middle Or- dovician age. The age of the dasts within any breccia bed is the same, as far as can be told, as the age of the interbedded black shale. Kindle and Whittington (1958, p. 341) suggested that the Cow Head Breccias are a type of flysch. They emphasized that there was no known source for many of the fossiliferous boulders since the equivalent carbonates of the shelf sequence are in large part very poorly fossiliferous.
Using the new information from the Taconics and west Newfoundland, Rodgers and Neate (1963) reinterpreted the Humber Arm Group as two large klippen, thereby bringing to fruition Logan's original concept. They drew a detailed strati graphic and structural analogy between the two Newfoundland ktippen and the Taconic Klippe and suggested that the New- foundland klippen were emplaced by gravity sliding from a source to the east of the Long Range. These authors were the first to include the igneous rocks of the Bay of Islands and Hare Bay in the trans- ported rocks, though they still assumed that these intruded the sediments of the Humber Arm, a relationship apparently confirmed by the detailed mapping of Smith (1958).
The age of sliding was deduced as Middle Ordovician, since the youngest rocks on which the klippen rest are of Middle Ordovician age. The Long Point Formation, of tate Middle Ordovician age, was inter- preted as a neoautochthonous cover, so that the Humber Arm altochton was emptaced in Middle Ordovician times. Rodgers (1965) later con- firmed the neoautochthonous nature of the Long Point. It should be noted, however, that, given the relationships described by Rodgers (1965) it was possible that the emplacement was later than the age of the Long Point since it is possible, if improbable, that the Long Point was transported on top of the Humber Arm allochthon. The likelihood of this possibility was lessened by Stevens (1970) who suggested that there might be a continuous section between the Table Head and the Long Point in the Mainland area of the Port-au- Port Peninsula though the critical part of the section was under the sea.
Rodgers and Neale (1963) concluded that the klippen could not have slid from the Long Range since the Precambrian rocks are surrounded by autochthonous rocks. A much more probable source lay east of White Bay in the Burlington Peninsula area. According to this view, the Humber Arm Supergroup is the unmetamorphosed equivalent of at least part of the Fleur de Lys Supergroup which must. if this is true, have been deformed and metamorphosed during or after the emplacement of the allochthons. An alternative view. also presented by Rodgers and Neale (1963). is that the Fleur de Lys is a Precambrian basement from which the allochthons slid. Much depends on the source of the allochthons and this matter will be discussed in more detail later.
Lilly (1964) urged caution in accepting the klippen hypothesis and commented that several other hypotheses were equally plausible given the information then available. Unfortunately Lilly, who had probably seen more of the rocks of west Newfoundland than any other geologist, never presented his ideas in detail. However, from incomplete manu- scripts (Lilly. 1967), compiled by W. Bruckner, it appears that Lilly thought that much of the Humber Arm was in place and older than the Carbonate rocks, although he did allow that some of the upper units could have been thrust from the west. Rodgers and Neale's (1963) klippen hypothesis stimulated a flurry of new work. Stevens (1965) mapped in the Humber Arm area and succeeded in dividing the Humber Arm rocks into several formations. He found fossils that suggested that the rocks ranged in age from early Cambrian to perhaps Middle Ordovician. Rocks much like the Green Point Series were found in the Tremadocian part of the succession. Spectacular melange zones, mapped as zones of chaotic deformation-, were found at the base of the atlochthon and at different horizons within it. They were interpreted as marking thrust zones so that the altochthon was constructed of several discrete slices. The melanges were thought to develop in zones of high hydrostatic pressure developed during movement. In such zones friction would be low. This interpretation of melange was at the time unusual since most workers interpreted such rocks as sedimentary deposits (Zen, 1961, Bruckner, 1966). Misled by the coarse grained nature of the lower and upper units of the Humber Arm, Stevens (1965) suggested that the Humber Arm largely formed in a deltaic environment. He did, however, confirm Rodgers and Neale's klippen hypothesis in the Humber Arm type area. Further evolution of thought on the geological evolution of west Newfoundland awaited developments in the realm of continental drift and plate tectonic theory. Early on, the former unity of the Appalachians and Caledonides was recognized by Wegener(1923) and Baitey (1927, 1929). Schuchert (1928), however, strongly denied any similarity and, as is well known, the hypothesis of Continental Drift passed into obscurity. Wilson (1962) suggested that the Cabot Fault and the Great Glen Fault of Scotland were once connected and analagous to the San Andreas Fault  in California. Church (1965) correlated the geology of the British Isles with that of Newfoundland. Perhaps his most significant correlation was that of the metamorphic rocks of the Scottish High- lands and Ireland with similar rocks on the Burlington Peninsula. Wilson published an important paper in 1966 in which he introduced the name "Proto Atlantic". Geologists studying the American Appalachians were reverting to Logan's view that the Appalachians somehow formed at an ancient continental margin (Drake et at, 1959; Dietz, 1963; Dietz and Holden, 1966). This concept was in agreement with the hypothesis of continental growth by the accretion of marginal orogens. These concepts were not popular outside North America for, in many other parts of the world, orogens seem to be intracratonic. Even in North America there were growing suspicions that the Appalachians had in fact an eastern craton and were not open to the Atlantic (Williams, 1964). How can orogens form at continental margins if they are bounded by older basement and some are intracratonic?
Wilson solved this dilemma by invoking ancient continental drift. He suggested that the Appalachian/Caledonian system is the suture zone in which a Proto Atlantic ocean was destroyed. Later continental drift has disrupted the orogen transposing parts of Paleo-Europe and Pateo-North America. For no good reason, Wilson shows the island arcs produced during the closure of the Proto Atlantic as fringing the North American Continent. As far as the writer is aware, it was W. Fritz who first suggested the possibility that the movement of the west Newfoundland allochthons was related to the closure of the Proto Atlantic. This suggestion was made in a private discussion after the writer had given a talk to the Logan Club of the Geological Survey of Canada on the geology of west Newfoundland. Unfortunately at the time he underrated its importance.
The whole matter of trans North Atlantic correlations was dis- cussed in detail at the Gander Conference (Kay, 1969), conceived and organized by Marshal Kay and convened in 1967. During this conference it became clear that there was overwhelming evidence that the Appalachians and the Catedonides were once part of the same orogenic belt and this paved the way for the later reinterpretation of Newfoundland geology in terms of the much better known geology of north west Europe.
At the Gander Conference, Stevens (1967a)reintroduced Murray's use of the term "ophiolite" for the Hare Bay and Bay of Islands Igneous Complexes but with no genetic implications. He also suggested that the Goose Cove Schists under the Hare Bay Complex were the equivalents of the Birchy Schists of the Fleur de Lys Supergroup (Church, 1969). This was thought to be evidence for the pre-Middle Ordovician deformation and metamorphism of the Fleur de Lys Supergroup as well as producing the first direct link between the geology of the Burlington Peninsula and that of west Newfoundland. Stevens (19671?) also demonstrated to the conferees the geology of the Humber Arm type section and a newly discovered section through the base of the allochthon north of The Gravels west of Stephenville.
The realization came in 1968 that the ophiolites did not in- trude the sediments on which they rest but were thrust sheets in their own right (Church and Stevens, 1968). This interpretation is self- evident in Hare Bay where Cooper (1937) had mapped the thrusts under the Goose Cove Schists. In the Bay of Islands area. the discovery of abundant detrital chromite and some serpentinite fragments in the Blow me Down Brook Formation under the igneous rocks and in the clastic rocks above the Table Head pointed to the same conclusion. The clastic sediments were, in part, derived from the ophiolites as they were transported. A field trip to Gaspe in 1968 (Stevens. ms. 1969) confirmed a suspicion that Logan's Tourell sandstones were analogous to the Blow me Down Brook Formation and are a ftysch deposit derived in part from an ophiotite source terraine. This also implied that the ophiolites were Arenig or older and not Devonian.
The similarity of the Quebec and Newfoundland ophiolite sequences to those of Papua (Davies. 1968). Cyprus (Gass. 1968) and Oman (Rein- hardt, 1969) was finally recognized in 1969 (Stevens et aL 1969). Since these ophiolites were described as oceanic crust and mantle sequences. it was logical to suggest that the Appalachian ophiolites had an oceanic origin.
This concept was expanded by Stevens (1969, 1970). After visiting the Gaspesian sections of the Quebec Group with J. Lajoie, C. Hubert, G. Middteton and R. Walker in 1969. it was realized that much of the Humber Arm Supergroup could be interpreted as part of a continental rise prism of deep water turbidites. If this were so, the autochthonous sequence would represent a continental shelf sucession. In 1969, the writer was not aware that this was Logan's original inter- pretation (Stevens, 1974).
In 1969, then, continental shelf and continental rise sediments had been recognized in west Newfoundland as well as probable oceanic crust and mantle. It was logical to try and incorporate these elements into a tectonic scheme based on Witson's concept of a Proto Atlantic. This was done in Stevens (1970). This paper made the following suggestions:
1. The geological relationships in west Newfoundland could be explained by assuming that the autochthonous sequence was a Cambro-Ordovician shelf sequence. The transported Humber Arm Supergroup was part of a continental rise prism. The Fleur de Lys Supergroup was the rest of the rise prism. The ophiolites were oceanic crust/mantle sequence that once floored part of Witson's Proto Atlantic.
2. After initiation in tate Proterozoic or Early Cambrian times, the ancient margin of North America remained essentially stable until latest Arenig times.
3. In late Arenig times, the shelf sequence was uplifted to give rise to the Table 'Head/St. George disconformity. At this same time flysch derived from the east appeared in the Humber Arm Supergroup. Late Arenig times, therefore, marked an important change in the history of the ancient continental margin in North America.
4. After this time the shelf broke up and sank. The rocks above the Table Head/St. George disconformity show a progressive in- crease in depth of deposition. Rocks much tike the Humber Arm formed and led some previous geologists to the belief that a11 of the Humber Arm Supergroup was in place. These fades changes are a striking example of the workings of Watther's law. 5. The ophiolites were a prime cause of movement of the Humber Arm Supergroup. As they moved westwards they peeled off packets of the rise sediments. Figure 6 of Stevens (1970) is not too dissimilar to recent diagrams of the structure of trench re- gions (e.g. Seely et a1_, 1974, fig. 2).
6. As the ophiolites moved westwards they shed detritus in front of them in the form of a flysch fan. This fan progressively migrated westwards and transgressed onto the now foundered shelf sequence during the Middle Ordovician. The movement of the allochthons was, therefore, a drawn out process, lasting several graptotite zones.
7. It seemed possible that the ophiolites of west Newfoundland once were continuous with those of the Burlington Peninsula so that it was possible that the deformation and metamorphism of the Fleur de Lys Supergroup was related to the ophiolite obduction. 8. Since detritus from the highest, ophiolite, sheet occurs in all of the internally derived flysch sequences it appears probable that the slice complex was progressively assembled and arrived at its final resting place in west Newfoundland in an already assembled condition.
9. In general, the stacking order of the slices reflects their paleogeographic position. The highest slice, the ophiolites, is farthest travelled and the lowest slices, locally parautochthonous shelf carbonates, are the least travelled. This again implies the slices were detached from their substrate in an order inverse to the stacking order.
Church and Stevens (1970, 1971) emphasized the oceanic origin of the Newfoundland ophiolites and suggested that they were emplaced as a result of the collision of the ancient margin of North America with a southeasterly dipping subduction zone. They drew a detailed com- parison between the ophiolite stratigraphy and the geophysical layering of modern ocean basins. According to this scheme the ultramafic rocks represent the upper mantle, the overlying gabbros and sheeted dikes represent layer 3 of the oceanic crust and the pillow lavas and sediments layers 2 and 1. The metamorphic rocks under the ophio- lites of west Newfoundland were thought to be produced either as a result of frictional heating during obduction or as a result of ob- duction of hot  (1000°C) ophiolite. This latter hypothesis would imply that the ophiolites were formed by sea floor spreading only shortly before obduction. This in turn opened the possibility that the ophiolites formed in a small ocean basin rather than in a major ocean basin such as the present Atlantic.
It was further suggested that some of the volcanic rocks of Notre Dame Bay were once continuous with the Bale Vert and Be ts Cove ophiolites but have an island arc complex built on them. The spectactular sheeted dyke unit of the Be ts Cove ophiolite was first recorded in this paper and, if the conclusions are correct, it is possible to study the Moho on land without deep drilling. Church (1972) later gave a more substantial account of the ophiolite problem.
Synchronous with the work at the University of Western Ontario. Dewey and Bird published an important series of papers on the same general problem (Dewey. 1969; Bird and Dewey, 1970; Dewey and Bird, 1971). These papers discussed the origin of the Appalachian/Cale- donian system in terms of plate tectonics, which then was only recently developed. Indeed, as far as the writer is aware, Dewey's 1969 paper was the first to apply plate tectonics to an ancient orogen. The earlier papers (Dewey, 1969; Bird and Dewey, 1970) differ from the interpretations of Church and Stevens in two main ways. The ophiolites found west of Notre Dame Bay were regarded as intrusive igneous bodies derived as diapirs from a subduction zone. The second point of difference concerned the polarity of subduction. According to Dewey (1969) and Bird and Dewey (1970) subduction was directed in a generally western direction, that is under the North American continent so that the ancient continental margin would have had the character of an Andean mountain range. This is difficult to accept since there are no post Lower Cambrian intrusions in west Newfound- land and terrestrial sedimentation did not commence in west Newfound- land until the late Silurian, early Devonian deposition of the Clam Bank Formation. The problem of polarity of subduction is explained in more detail in a later section.
By late 1971 Dewey and Bird (1971) had accepted the Stevens (1970) and Church and Stevens (1970, 1971) interpretation of the western ophiolites but suggested that they formed in a small ocean basin above a west dipping subduction zone.
Later works (Williams, 1971, 1972; Upadyuay et al, 1971; Williams and Malpas. 1972; Williams and Smyth. 1973; Norman and Strong, 1975; and Riccio, 1976) have substantially supported the oceanic origin of the western ophiolites. It is now also generally accepted that the sedimentary rocks of west Newfoundland represent a telescoped continental margin of Cambro-Ordovician age and that sedimentary and tectonic evolution of the region is somehow related to a cycle of birth and destruction of an Early Paleozoic ocean; that is, a Wilson Cycle.
The second part of this thesis is devoted to a discussion of the second generation of plate tectonic hypothesis based on the geology of west Newfoundland.